Oracle® Database

Application Developer's Guide - Large Objects

10g Release 2 (10.2)

Part No. B14249-01

June 2005

Oracle Database Application Developer's Guide - Large Objects 10g Release 2 (10.2)

Part No. B14249-01

Copyright © 1996, 2005, Oracle. All rights reserved.

Primary Authors: Jack Melnick, Eric Paapanen

Contributing Authors:  K. Akiyama, Geeta Arora, S. Banerjee, Yujie Cao, Thomas H. Chang, E. Chong, S. Das, C. Freiwald, C. Iyer, M. Jagannath, R. Krishnan, M. Krishnaprasad, S. Lari, Li-Sen Liu, D. Mullen, V. Nimani, A. Roy, S. Shah, A. Shivarudraiah, J. Srinivasan, R. Toohey, Anh-Tuan Tran, G. Viswana, A. Yalamanchi

Contributors:  J. Balaji, Debarun Banerjee, Subhranshu Banerjee, D. Cruceanu, M. Chien, G. Edmiston, M. Fry, J. Kalogeropoulos, M. Kamani, S. Kotsovolos, K. Kunchithapadam, Geoff Lee, Scott Lynn, P. Manavazhi, S. Muthulingam, R. Ratnam, C. Shay, A. Shehade, E. Shirk, Jan Syssauw, S. Vedala, E. Wan, J. Yang

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Contents

Title and Copyright Information

Preface

Audience

Documentation Accessibility

Related Documents

Conventions

What's New in Large Objects?

LOB Features Introduced in Oracle Database 10g Release 2

Restrictions Removed in Oracle Database 10g Release 2

LOB Features Introduced in Oracle Database 10g Release 1

Restrictions Removed in Oracle Database 10g Release 1

LOB Features Introduced in Oracle9i Release 2

Restrictions Removed in Oracle9i Release 2

LOB Features Introduced in Oracle9i Release 1

Restrictions Removed in Oracle9i Release 1

Part I Getting Started

1 Introduction to Large Objects

What Are Large Objects?

Why Use Large Objects?

Using LOBs for Semi-structured Data

Using LOBs for Unstructured Data

Why Not Use LONGs? Different Kinds of LOBs

Internal LOBs

External LOBs and the BFILE Datatype

Introducing LOB Locators Database Semantics for Internal and External LOBs Large Object Datatypes Object Datatypes and LOBs Storing and Creating Other Datatypes with LOBs

VARRAYs Stored as LOBs

XMLType Columns Stored as CLOBs

LOBs Used in Oracle interMedia

2 Working with LOBs

LOB Column States

Locking a Row Containing a LOB

Opening and Closing LOBs

LOB Locator and LOB Value

Using the Data Interface for LOBs

Using the LOB Locator to Access and Modify LOB Values

LOB Locators and BFILE Locators

Table print_media

Initializing a LOB Column to Contain a Locator

Initializing a Persistent LOB Column

Initializing BFILEs

Accessing LOBs

Accessing a LOB Using SQL

Accessing a LOB Using the Data Interface

Accessing a LOB Using the Locator Interface

LOB Rules and Restrictions

Rules for LOB Columns

Restrictions for LOB Operations

3 Managing LOBs: Database Administration

Database Utilities for Loading Data into LOBs

Using SQL*Loader to Load LOBs

Using SQL*Loader to Populate a BFILE Column

Using Oracle DataPump to Transfer LOB Data

Managing Temporary LOBs

Managing Temporary Tablespace for Temporary LOBs

Managing BFILEs

Rules for Using Directory Objects and BFILEs

Setting Maximum Number of Open BFILEs

Changing Tablespace Storage for a LOB
Part II Application Design

4 LOBs in Tables

Creating Tables That Contain LOBs

Initializing Persistent LOBs to NULL or Empty

Setting a Persistent LOB to NULL

Setting a Persistent LOB to Empty

Initializing LOBs Initializing Persistent LOB Columns and Attributes to a Value Initializing BFILEs to NULL or a File Name Restriction on First Extent of a LOB Segment Choosing a LOB Column Datatype

LOBs Compared to LONG and LONG RAW Types

Storing Varying-Width Character Data in LOBs

Implicit Character Set Conversions with LOBs

Selecting a Table Architecture LOB Storage

Inline and Out-of-Line LOB Storage

Defining Tablespace and Storage Characteristics for Persistent LOBs

Assigning a LOB Data Segment Name

LOB Storage Characteristics for LOB Column or Attribute TABLESPACE and LOB Index

Tablespace for LOB Index in Non-Partitioned Table

PCTVERSION RETENTION CACHE / NOCACHE / CACHE READS

CACHE / NOCACHE / CACHE READS: LOB Values and Buffer Cache

LOGGING / NOLOGGING

LOBs Will Always Generate Undo for LOB Index Pages

When LOGGING is Set Oracle Will Generate Full Redo for LOB Data Pages

CHUNK

Choosing the Value of CHUNK

Set INITIAL and NEXT to Larger than CHUNK

ENABLE or DISABLE STORAGE IN ROW Clause Guidelines for ENABLE or DISABLE STORAGE IN ROW Indexing LOB Columns

Using Domain Indexing on LOB Columns

Indexing LOB Columns Using a Text Index

Function-Based Indexes on LOBs

Extensible Indexing on LOB Columns

Extensible Optimizer

Oracle Text Indexing Support for XML Manipulating LOBs in Partitioned Tables

Partitioning a Table Containing LOB Columns

Creating an Index on a Table Containing Partitioned LOB Columns

Moving Partitions Containing LOBs

Splitting Partitions Containing LOBs

Merging Partitions Containing LOBs

LOBs in Index Organized Tables Restrictions for LOBs in Partitioned Index-Organized Tables Updating LOBs in Nested Tables
5 Advanced Design Considerations

LOB Buffering Subsystem

Advantages of LOB Buffering

Guidelines for Using LOB Buffering

LOB Buffering Subsystem Usage

LOB Buffer Physical Structure

LOB Buffering Subsystem Usage Scenario

Flushing the LOB Buffer Flushing the Updated LOB Using Buffer-Enabled Locators Saving Locator State to Avoid a Reselect OCI Example of LOB Buffering Opening Persistent LOBs with the OPEN and CLOSE Interfaces

Index Performance Benefits of Explicitly Opening a LOB

Working with Explicitly Open LOB Instances

Read Consistent Locators

A Selected Locator Becomes a Read Consistent Locator

Example of Updating LOBs and Read-Consistency

Example of Updating LOBs Through Updated Locators

Example of Updating a LOB Using SQL DML and DBMS_LOB

Example of Using One Locator to Update the Same LOB Value

Example of Updating a LOB with a PL/SQL (DBMS_LOB) Bind Variable

LOB Locators and Transaction Boundaries

Reading and Writing to a LOB Using Locators

Selecting the Locator Outside of the Transaction Boundary

Selecting the Locator Within a Transaction Boundary

LOB Locators Cannot Span Transactions

Example of Locator Not Spanning a Transaction

LOBs in the Object Cache Terabyte-Size LOB Support

Maximum Storage Limit for Terabyte-Size LOBs

Using Terabyte-Size LOBs with JDBC

Using Terabyte-Size LOBs with the DBMS_LOB Package

Using Terabyte-Size LOBs with OCI

Guidelines for Creating Gigabyte LOBs

Creating a Tablespace and Table to Store Gigabyte LOBs

6 Overview of Supplied LOB APIs

Programmatic Environments That Support LOBs

Comparing the LOB Interfaces

Using PL/SQL (DBMS_LOB Package) to Work with LOBs

Provide a LOB Locator Before Running the DBMS_LOB Routine

Guidelines for Offset and Amount Parameters in DBMS_LOB Operations

Determining Character Set ID

PL/SQL Functions and Procedures for LOBs

PL/SQL Functions and Procedures to Modify LOB Values

PL/SQL Functions and Procedures for Introspection of LOBs

PL/SQL Operations on Temporary LOBs

PL/SQL Read-Only Functions and Procedures for BFILEs

PL/SQL Functions and Procedures to Open and Close Internal and External LOBs

Using OCI to Work with LOBs

Setting the CSID Parameter for OCI LOB APIs

Fixed-Width and Varying-Width Character Set Rules for OCI

Other Operations

NCLOBs in OCI

OCILobLoadFromFile2() Amount Parameter OCILobRead2() Amount Parameter OCILobLocator Pointer Assignment LOB Locators in Defines and Out-Bind Variables in OCI OCI Functions That Operate on BLOBs, CLOBs, NCLOBs, and BFILEs OCI Functions to Modify Persistent LOB (BLOB, CLOB, and NCLOB) Values OCI Functions to Read or Examine Persistent LOB and External LOB (BFILE) Values OCI Functions for Temporary LOBs OCI Read-Only Functions for BFILEs OCI LOB Locator Functions OCI LOB-Buffering Functions OCI Functions to Open and Close Internal and External LOBs OCI LOB Examples Further Information About OCI Using C++ (OCCI) to Work with LOBs

OCCI Classes for LOBs

Clob Class

Blob Class

Bfile Class

Fixed-Width Character Set Rules Varying-Width Character Set Rules Offset and Amount Parameters for Other OCCI Operations

NCLOBs in OCCI

Amount Parameter for OCCI LOB copy() Methods Amount Parameter for OCCI read() Operations Further Information About OCCI OCCI Methods That Operate on BLOBs, BLOBs, NCLOBs, and BFILEs OCCI Methods to Modify Persistent LOB (BLOB, CLOB, and NCLOB) Values OCCI Methods to Read or Examine Persistent LOB and BFILE Values OCCI Read-Only Methods for BFILEs Other OCCI LOB Methods OCCI Methods to Open and Close Internal and External LOBs Using C/C++ (Pro*C) to Work with LOBs

First Provide an Allocated Input Locator Pointer That Represents LOB

Pro*C/C++ Statements That Operate on BLOBs, CLOBs, NCLOBs, and BFILEs

Pro*C/C++ Embedded SQL Statements to Modify Persistent LOB Values

Pro*C/C++ Embedded SQL Statements for Introspection of LOBs

Pro*C/C++ Embedded SQL Statements for Temporary LOBs

Pro*C/C++ Embedded SQL Statements for BFILEs

Pro*C/C++ Embedded SQL Statements for LOB Locators

Pro*C/C++ Embedded SQL Statements for LOB Buffering

Pro*C/C++ Embedded SQL Statements to Open and Close LOBs

Using COBOL (Pro*COBOL) to Work with LOBs

First Provide an Allocated Input Locator Pointer That Represents LOB

Pro*COBOL Statements That Operate on BLOBs, CLOBs, NCLOBs, and BFILEs

Pro*COBOL Embedded SQL Statements to Modify Persistent LOB Values

Pro*COBOL Embedded SQL Statements for Introspection of LOBs

Pro*COBOL Embedded SQL Statements for Temporary LOBs

Pro*COBOL Embedded SQL Statements for BFILEs

Pro*COBOL Embedded SQL Statements for LOB Locators

Pro*COBOL Embedded SQL Statements for LOB Buffering

Pro*COBOL Embedded SQL Statements for Opening and Closing LOBs and BFILEs

Using Visual Basic (Oracle Objects for OLE) to Work with LOBs

OO4O Syntax Reference

OraBlob, OraClob, and OraBfile Object Interfaces Encapsulate Locators

OraBlob and OraClob Objects Are Retrieved as Part of Dynaset

Use the Clone Method to Retain Locator Independent of the Dynaset Move

Example of OraBlob and OraBfile OO4O Methods and Properties to Access Data Stored in LOBs OO4O Methods to Modify BLOB, CLOB, and NCLOB Values OO4O Methods to Read or Examine Internal and External LOB Values OO4O Methods to Open and Close External LOBs (BFILEs) OO4O Methods for Persistent LOBBuffering OO4O Properties for Operating on LOBs OO4O Read-Only Methods for External Lobs (BFILEs) OO4O Properties for Operating on External LOBs (BFILEs) Using Java (JDBC) to Work with LOBs

Modifying Internal Persistent LOBs Using Java

Reading Internal Persistent LOBs and External LOBs (BFILEs) with Java

BLOB, CLOB, and BFILE Classes

Calling DBMS_LOB Package from Java (JDBC) Referencing LOBs Using Java (JDBC)

Using OracleResultSet: BLOB and CLOB Objects Retrieved

JDBC Syntax References and Further Information JDBC Methods for Operating on LOBs JDBC oracle.sql.BLOB Methods to Modify BLOB Values JDBC oracle.sql.BLOB Methods to Read or Examine BLOB Values JDBC oracle.sql.BLOB Methods and Properties for BLOB Buffering JDBC oracle.sql.CLOB Methods to Modify CLOB Values JDBC oracle.sql.CLOB Methods to Read or Examine CLOB Value JDBC oracle.sql.CLOB Methods and Properties for CLOB Buffering JDBC oracle.sql.BFILE Methods to Read or Examine External LOB (BFILE) Values JDBC oracle.sql.BFILE Methods and Properties for BFILE Buffering JDBC Temporary LOB APIs JDBC: Opening and Closing LOBs JDBC: Opening and Closing BLOBs

Opening the BLOB Using JDBC

Checking If the BLOB Is Open Using JDBC

Closing the BLOB Using JDBC

JDBC: Opening and Closing CLOBs

Opening the CLOB Using JDBC

Checking If the CLOB Is Open Using JDBC

Closing the CLOB Using JDBC

JDBC: Opening and Closing BFILEs

Opening BFILEs

Checking If the BFILE Is Open

Closing the BFILE

Usage Example (OpenCloseLob.java)

Truncating LOBs Using JDBC

JDBC: Truncating BLOBs

JDBC: Truncating CLOBs

JDBC BLOB Streaming APIs JDBC CLOB Streaming APIs BFILE Streaming APIs

JDBC BFILE Streaming Example (NewStreamLob.java)

JDBC and Empty LOBs Oracle Provider for OLE DB (OraOLEDB) Overview of Oracle Data Provider for .NET (ODP.NET)
7 Performance Guidelines

LOB Performance Guidelines

Chunk Size

Performance Guidelines for Small LOBs

General Performance Guidelines

Temporary LOB Performance Guidelines

Performance Considerations for SQL Semantics and LOBs

Moving Data to LOBs in a Threaded Environment LOB Access Statistics

Example of Retrieving LOB Access Statistics

Part III SQL Access to LOBs

8 DDL and DML Statements with LOBs

Creating a Table Containing One or More LOB Columns

Creating a Nested Table Containing a LOB

Inserting a Row by Selecting a LOB From Another Table

Inserting a LOB Value Into a Table

Inserting a Row by Initializing a LOB Locator Bind Variable

PL/SQL: Inserting a Row by Initializing a LOB Locator Bind Variable

C (OCI): Inserting a Row by Initializing a LOB Locator Bind Variable

COBOL (Pro*COBOL): Inserting a Row by Initializing a LOB Locator Bind Variable

C/C++ (Pro*C/C++): Inserting a Row by Initializing a LOB Locator Bind Variable

Visual Basic (OO4O): Inserting a Row by Initializing a LOB Locator Bind Variable

Java (JDBC): Inserting a Row by Initializing a LOB Locator Bind Variable

Updating a LOB with EMPTY_CLOB() or EMPTY_BLOB() Updating a Row by Selecting a LOB From Another Table
9 SQL Semantics and LOBs

Using LOBs in SQL

SQL Functions and Operators Supported for Use with LOBs

UNICODE Support

Codepoint Semantics

Return Values for SQL Semantics on LOBs

LENGTH Return Value for LOBs

Implicit Conversion of LOB Datatypes in SQL

Implicit Conversion Between CLOB and NCLOB Datatypes in SQL

Unsupported Use of LOBs in SQL VARCHAR2 and RAW Semantics for LOBs

LOBs Returned from SQL Functions

IS NULL and IS [NOT] NULL Usage with VARCHAR2s and CLOBs

WHERE Clause Usage with LOBs

10 PL/SQL Semantics for LOBs

PL/SQL Statements and Variables

Implicit Conversions Between CLOB and VARCHAR2

Explicit Conversion Functions

VARCHAR2 and CLOB in PL/SQL Built-In Functions

PL/SQL CLOB Comparison Rules

CLOBs Follow the VARCHAR2 Collating Sequence

11 Migrating Columns from LONGs to LOBs

Benefits of Migrating LONG Columns to LOB Columns

Preconditions for Migrating LONG Columns to LOB Columns

Dropping a Domain Index on a LONG Column Before Converting to a LOB

Preventing Generation of Redo Space on Tables Converted to LOB Datatypes

Using utldtree.sql to Determine Where Your Application Needs Change Converting Tables from LONG to LOB Datatypes

Using ALTER TABLE to Convert LONG Columns to LOB Columns

Migration Issues

Copying a LONG to a LOB Column Using the TO_LOB Operator Online Redefinition of Tables with LONG Columns Migrating Applications from LONGs to LOBs

LOB Columns Are Not Allowed in Clustered Tables

LOB Columns Are Not Allowed in UPDATE OF Triggers

Indexes on Columns Converted from LONG to LOB Datatypes

Empty LOBs Compared to NULL and Zero Length LONGs

Overloading with Anchored Types

Some Implicit Conversions Are Not Supported for LOB Datatypes

Part IV Using LOB APIs

12 Operations Specific to Persistent and Temporary LOBs

Persistent LOB Operations

Inserting a LOB into a Table

Selecting a LOB from a Table

Temporary LOB Operations

Creating and Freeing a Temporary LOB

Creating Persistent and Temporary LOBs in PL/SQL
13 Data Interface for Persistent LOBs

Overview of the Data Interface for Persistent LOBs

Benefits of Using the Data Interface for Persistent LOBs

Using the Data Interface for Persistent LOBs in PL/SQL

Guidelines for Accessing LOB Columns Using the Data Interface in SQL and PL/SQL

Implicit Assignment and Parameter Passing

Passing CLOBs to SQL and PL/SQL Built-In Functions

Explicit Conversion Functions

Calling PL/SQL and C Procedures from SQL

Calling PL/SQL and C Procedures from PL/SQL

Binds of All Sizes in INSERT and UPDATE Operations

4000 Byte Limit on Results of a SQL Operator

Example of 4000 Byte Result Limit of a SQL Operator

Restrictions on Binds of More Than 4000 Bytes

Parallel DML Support for LOBs

Example: PL/SQL - Using Binds of More Than 4000 Bytes in INSERT and UPDATE

Using the Data Interface for LOBs with INSERT, UPDATE, and SELECT Operations

Using the Data Interface for LOBs in Assignments and Parameter Passing

Using the Data Interface for LOBs with PL/SQL Built-In Functions

Using the Data Interface for Persistent LOBs in OCI

Binding LOB Datatypes in OCI

Defining LOB Datatypes in OCI

Using Multibyte Character Sets in OCI with the Data Interface for LOBs

Using OCI Functions to Perform INSERT or UPDATE on LOB Columns

Simple INSERTs or UPDATEs in One Piece

Using Piecewise INSERTs and UPDATEs with Polling

Piecewise INSERTs and UPDATEs with Callback

Array INSERT and UPDATE Operations

Using the Data Interface to Fetch LOB Data in OCI

Simple Fetch in One Piece

Piecewise Fetch with Polling

Piecewise with Callback

Array Fetch

PL/SQL and C Binds from OCI

Calling PL/SQL Out-binds in the "begin foo(:1); end;" Manner

Calling PL/SQL Out-binds in the "call foo(:1);" Manner

Example: C (OCI) - Binds of More than 4000 Bytes for INSERT and UPDATE Using the Data Interface for LOBs in PL/SQL Binds from OCI on LOBs

Calling PL/SQL Out-binds in the "begin foo(:1); end;" Manner

Calling PL/SQL Out-binds in the "call foo(:1);" Manner

Binding LONG Data for LOB Columns in Binds Greater Than 4000 Bytes Binding LONG Data to LOB Columns Using Piecewise INSERT with Polling Binding LONG Data to LOB Columns Using Piecewise INSERT with Callback Binding LONG Data to LOB Columns Using an Array INSERT Selecting a LOB Column into a LONG Buffer Using a Simple Fetch Selecting a LOB Column into a LONG Buffer Using Piecewise Fetch with Polling Selecting a LOB Column into a LONG Buffer Using Piecewise Fetch with Callback Selecting a LOB Column into a LONG Buffer Using an Array Fetch Using the Data Interface for Persistent LOBs in Java Using the Data Interface with Remote LOBs

Remote Data Interface Example in PL/SQL

Remote Data Interface Example in OCI

Remote Data Interface Examples in JDBC

14 LOB APIs for Basic Operations

Supported Environments

Appending One LOB to Another

Determining Character Set Form

Determining Character Set ID

Loading a LOB with Data from a BFILE

Loading a BLOB with Data from a BFILE

Loading a CLOB or NCLOB with Data from a BFILE

PL/SQL: Loading Character Data from a BFILE into a LOB

PL/SQL: Loading Segments of Character Data into Different LOBs

Determining Whether a LOB is Open

Java (JDBC): Checking If a LOB Is Open

Checking If a CLOB Is Open

Checking If a BLOB Is Open

Displaying LOB Data Reading Data from a LOB LOB Array Read Reading a Portion of a LOB (SUBSTR) Comparing All or Part of Two LOBs Patterns: Checking for Patterns in a LOB Using INSTR Length: Determining the Length of a LOB Copying All or Part of One LOB to Another LOB Copying a LOB Locator Equality: Checking If One LOB Locator Is Equal to Another Determining Whether LOB Locator Is Initialized Appending to a LOB Writing Data to a LOB LOB Array Write Trimming LOB Data Erasing Part of a LOB Enabling LOB Buffering Flushing the Buffer Disabling LOB Buffering Determining Whether a LOB instance Is Temporary

Java (JDBC): Determining Whether a BLOB Is Temporary

Converting a BLOB to a CLOB Converting a CLOB to a BLOB
15 LOB APIs for BFILE Operations

Supported Environments for BFILE APIs

Accessing BFILEs

Directory Objects

Initializing a BFILE Locator

How to Associate Operating System Files with a BFILE

BFILENAME and Initialization Characteristics of the BFILE Datatype

DIRECTORY Name Specification

On Windows Platforms

BFILE Security

Ownership and Privileges

Read Permission on a DIRECTORY Object

SQL DDL for BFILE Security

SQL DML for BFILE Security

Catalog Views on Directories

Guidelines for DIRECTORY Usage

BFILEs in Shared Server (Multithreaded Server) Mode

External LOB (BFILE) Locators

When Two Rows in a BFILE Table Refer to the Same File

BFILE Locator Variable

Guidelines for BFILEs

Loading a LOB with BFILE Data Opening a BFILE with OPEN Opening a BFILE with FILEOPEN Determining Whether a BFILE Is Open Using ISOPEN Determining Whether a BFILE Is Open with FILEISOPEN Displaying BFILE Data Reading Data from a BFILE Reading a Portion of BFILE Data Using SUBSTR Comparing All or Parts of Two BFILES Checking If a Pattern Exists in a BFILE Using INSTR Determining Whether a BFILE Exists Getting the Length of a BFILE Assigning a BFILE Locator Getting Directory Object Name and File Name of a BFILE Updating a BFILE by Initializing a BFILE Locator Closing a BFILE with FILECLOSE Closing a BFILE with CLOSE Closing All Open BFILEs with FILECLOSEALL Inserting a Row Containing a BFILE
A LOB Demonstration Files

PL/SQL LOB Demonstration Files

OCI LOB Demonstration Files

Visual Basic OO4O LOB Demonstration Files

Java LOB Demonstration Files

Glossary

Index

Preface

This guide describes database features that support applications using Large Object (LOB) datatypes. The information in this guide applies to all platforms and does not include system-specific information.

This preface contains these topics:

- Audience

- Documentation Accessibility

- Related Documents

- Conventions

Audience

Oracle Database Application Developer's Guide - Large Objects is intended for programmers developing new applications that use LOBs, as well as those who have already implemented this technology and now want to take advantage of new features.

The increasing importance of multimedia data as well as unstructured data has led to this topic being presented as an independent volume within the Oracle Application Developers documentation set.

Feature Coverage and Availability

Oracle Database Application Developer's Guide - Large Objects contains information that describes the features and functionality of Oracle Database 10g.

What You Need To Use LOBs

The database includes all of the resources you need to use LOBs in your application; however, there are some restrictions on how you can use LOBs as described in the following:

See Also:

- "LOB Rules and Restrictions"

- "Restrictions Removed in Oracle Database 10g Release 2"

- "Restrictions for LOBs in Partitioned Index-Organized Tables"

Documentation Accessibility

Our goal is to make Oracle products, services, and supporting documentation accessible, with good usability, to the disabled community. To that end, our documentation includes features that make information available to users of assistive technology. This documentation is available in HTML format, and contains markup to facilitate access by the disabled community. Accessibility standards will continue to evolve over time, and Oracle is actively engaged with other market-leading technology vendors to address technical obstacles so that our documentation can be accessible to all of our customers. For more information, visit the Oracle Accessibility Program Web site at

http://www.oracle.com/accessibility/

Accessibility of Code Examples in Documentation

Screen readers may not always correctly read the code examples in this document. The conventions for writing code require that closing braces should appear on an otherwise empty line; however, some screen readers may not always read a line of text that consists solely of a bracket or brace.

Accessibility of Links to External Web Sites in Documentation

This documentation may contain links to Web sites of other companies or organizations that Oracle does not own or control. Oracle neither evaluates nor makes any representations regarding the accessibility of these Web sites.

TTY Access to Oracle Support Services

Oracle provides dedicated Text Telephone (TTY) access to Oracle Support Services within the United States of America 24 hours a day, seven days a week. For TTY support, call 800.446.2398.

Related Documents

For more information, see the following manuals:

- Oracle Database PL/SQL Packages and Types Reference: Use this book to learn PL/SQL and to get a complete description of this high-level programming language, which is a procedural extension to SQL.

- Oracle Call Interface Programmer's Guide: Describes Oracle Call Interface (OCI). You can use OCI to build third-generation language (3GL) applications in C or C++ that access Oracle Server.

- Oracle C++ Call Interface Programmer's Guide

- Pro*C/C++ Programmer's Guide: Oracle Corporation also provides the Pro* series of precompilers, which allow you to embed SQL and PL/SQL in your application programs.

- Pro*COBOL Programmer's Guide: The Pro*COBOL precompiler enables you to embed SQL and PL/SQL in your COBOL programs for access to Oracle Server.

- Programmer's Guide to the Oracle Precompilers and Pro*Fortran Supplement to the Oracle Precompilers Guide: Use these manuals for Fortran precompiler programming to access Oracle Server.

- Java: Oracle Database offers the opportunity of working with Java in the database. The Oracle Java documentation set includes the following:

- Oracle Database JDBC Developer's Guide and Reference

- Oracle Database Java Developer's Guide

- Oracle Database JPublisher User's Guide

Oracle Database error message documentation is only available in HTML. If you only have access to the Oracle Documentation CD, you can browse the error messages by range. Once you find the specific range, use your browser "find in page" feature to locate the specific message. When connected to the Internet, you can search for a specific error message using the error message search feature of the Oracle online documentation.

Many of the examples in this book use the sample schemas, which are installed by default when you select the Basic Installation option with an Oracle Database installation. Refer to Oracle Database Sample Schemas for information on how these schemas were created and how you can use them yourself.

Multimedia

You can access the Oracle development environment for multimedia technology in a number of different ways.

- To build self-contained applications that integrate with the database, you can learn about how to use the Oracle extensibility framework in Oracle Database Data Cartridge Developer's Guide

- To use the Oracle interMedia applications, refer to the following:

- Oracle interMedia Reference.

- Oracle interMedia Java Classes Reference

- Oracle Text Reference

- Oracle Text Application Developer's Guide

- Oracle interMedia Reference

Basic References

- For SQL information, see the Oracle Database SQL Reference and Oracle Database Administrator's Guide

- For information about using LOBs with Oracle XML DB, refer to Oracle XML DB Developer's Guide

- For information about Oracle XML SQL with LOB data, refer to Oracle Database Advanced Replication

- For basic Oracle concepts, see Oracle Database Concepts.

- For information on using Oracle Data Pump, SQL*Loader, and other database utilities, see Oracle Database Utilities

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Conventions

This section describes the conventions used in the text and syntax examples of this documentation set. It describes:

- Conventions in Text

- Conventions in Syntax Examples

Conventions in Text

We use various conventions in text to help you more quickly identify special terms. The following table describes those conventions and provides examples of their use.

Convention

Meaning

Example

Bold

Bold typeface indicates terms that are defined in the text or terms that appear in a glossary, or both.

When you specify this clause, you create an index-organized table.

Italics

Italic typeface indicates book titles or emphasis.

Oracle Database Concepts
Ensure that the recovery catalog and target database do not reside on the same disk.

UPPERCASE monospace (fixed-width font)

Uppercase monospace typeface indicates elements supplied by the system. Such elements include parameters, privileges, datatypes, RMAN keywords, SQL keywords, SQL*Plus or utility commands, packages and methods, as well as system-supplied column names, database objects and structures, usernames, and roles.

You can specify this clause only for a NUMBER column.
You can back up the database by using the BACKUP command.

Query the TABLE_NAME column in the USER_TABLES data dictionary view.

Use the DBMS_STATS.GENERATE_STATS procedure.

lowercase monospace (fixed-width font)

Lowercase monospace typeface indicates executables, filenames, directory names, and sample user-supplied elements. Such elements include computer and database names, net service names, and connect identifiers, as well as user-supplied database objects and structures, column names, packages and classes, usernames and roles, program units, and parameter values.
Note: Some programmatic elements use a mixture of UPPERCASE and lowercase. Enter these elements as shown.

Enter sqlplus to open SQL*Plus.
The password is specified in the orapwd file.

Back up the datafiles and control files in the /disk1/oracle/dbs directory.

The department_id, department_name, and location_id columns are in the hr.departments table.

Set the QUERY_REWRITE_ENABLED initialization parameter to true.

Connect as oe user.

The JRepUtil class implements these methods.

lowercase monospace (fixed-width font) italic

Lowercase monospace italic font represents placeholders or variables.

You can specify the parallel_clause.
Run Uold_release.SQL where old_release refers to the release you installed prior to upgrading.

Conventions in Syntax Examples

Syntax examples illustrate SQL, PL/SQL, SQL*Plus, or other command-line statements. They are displayed in a monospace (fixed-width) font and separated from normal text as shown in this example:

SELECT username FROM dba_users WHERE username = 'MIGRATE'
;

The following table describes typographic conventions used in syntax examples and provides examples of their use.

Convention

Meaning

Example

[ ]

Brackets enclose one or more optional items. Do not enter the brackets.

DECIMAL (digits [ , precision ])

{ }

Braces enclose two or more items, one of which is required. Do not enter the braces.

{ENABLE | DISABLE}

|

A vertical bar represents a choice of two or more options within brackets or braces. Enter one of the options. Do not enter the vertical bar.

{ENABLE | DISABLE}
[COMPRESS | NOCOMPRESS]

...

Horizontal ellipsis points indicate either:

- That we have omitted parts of the code that are not directly related to the example

- That you can repeat a portion of the code

CREATE TABLE ... AS subquery;

SELECT col1, col2, ... , coln FROM employees;

.
.
.

Vertical ellipsis points indicate that we have omitted several lines of code not directly related to the example.

SQL> SELECT NAME FROM V$DATAFILE;
NAME
------------------------------------
/fsl/dbs/tbs_01.dbf
/fs1/dbs/tbs_02.dbf
.
.
.
/fsl/dbs/tbs_09.dbf
9 rows selected.

Other notation

You must enter symbols other than brackets, braces, vertical bars, and ellipsis points as shown.

acctbal NUMBER(11,2);
acct CONSTANT NUMBER(4) := 3;

Italics

Italicized text indicates placeholders or variables for which you must supply particular values.

CONNECT SYSTEM/system_password
DB_NAME = database_name

UPPERCASE

Uppercase typeface indicates elements supplied by the system. We show these terms in uppercase in order to distinguish them from terms you define. Unless terms appear in brackets, enter them in the order and with the spelling shown. However, because these terms are not case sensitive, you can enter them in lowercase.

SELECT last_name, employee_id FROM employees;
SELECT * FROM USER_TABLES;

DROP TABLE hr.employees;

lowercase

Lowercase typeface indicates programmatic elements that you supply. For example, lowercase indicates names of tables, columns, or files.
Note: Some programmatic elements use a mixture of UPPERCASE and lowercase. Enter these elements as shown.

SELECT last_name, employee_id FROM employees;
sqlplus hr/hr

CREATE USER mjones IDENTIFIED BY ty3MU9;

What's New in Large Objects?

This section describes the new features in the following releases:

- LOB Features Introduced in Oracle Database 10g Release 2

- Restrictions Removed in Oracle Database 10g Release 2

- LOB Features Introduced in Oracle Database 10g Release 1

- Restrictions Removed in Oracle Database 10g Release 1

- LOB Features Introduced in Oracle9i Release 2

- RestrictionsRemoved in Oracle9i Release 2

- LOB Features Introduced in Oracle9i Release 1

- Restrictions Removed in Oracle9i Release 1

LOB Features Introduced in Oracle Database 10g Release 2

Insert, update, and select of remote LOBs is supported, subject to some remaining restrictions.

See Also:

- "LOB Rules and Restrictions" for changes

- "Using the Data Interface with Remote LOBs"

Read and write of LOB data for multiple locators is supported by new OCI functions.

See Also:

- "LOB Array Read"

- "LOB Array Write"

The JDBC 3.0 API is now supported for Java access to LOBs.

See Also:

"Using Java (JDBC) to Work with LOBs"

The Data Interface is now supported in Java.

See Also:

"Using the Data Interface for Persistent LOBs in Java"

Some phases of online redefinition of LONG-to-LOB migration can execute in parallel.

See Also:

- "Parallel Online Redefinition"

- "Parallel DML Support for LOBs"

Directory objects can be managed by Enterprise Manager Web console.

See Also:

"Directory Objects"

Three new LOB session-level statistics are now available to users: LOB reads, LOB writes, and LOB writes unaligned.

See Also:

"LOB Access Statistics"

Restrictions Removed in Oracle Database 10g Release 2

The following restrictions on LOB features were removed in Oracle Database 10g Release 2.

- You can initialize a LOB attribute to character or raw data of any size. Earlier, this feature was available only for top-level LOB columns.

See "Initializing Persistent LOB Columns and Attributes to a Value "

- Select of remote LOB data defined as character or raw datatype is supported for the OCI, JDBC, and PL/SQL interfaces.

See "Using the Data Interface with Remote LOBs".

LOB Features Introduced in Oracle Database 10g Release 1

The following features are introduced in Oracle Database 10g Release 1 (10.1):

- Increased LOB Size Limit

The maximum size limit for LOBs is 8 to 128 terabytes, depending on your database block size. The following APIs support this new size limit:

- DBMS_LOB PL/SQL package

- OCI

- JDBC

Previous releases supported LOBs up to a maximum size of 4 GB. For details see "Terabyte-Size LOB Support".

- Performance Enhancements

A number of performance enhancements have been added for this release including:

- LOB performance in INSERT, UPDATE, and SELECT operations is greatly enhanced in this release. For more information on maximizing LOB performance, see "Temporary LOB Performance Guidelines".

- Direct support for LOBs in the JDBC Thin driver.

The JDBC Thin driver now provides direct support for BFILEs, BLOBs, and CLOBs. Prior to this release, it supported them through calls to PL/SQL routines.

- Heterogeneous Cross-Platform Transportable Tablespace Support for LOBs

Support for LOBs in heterogeneous cross-platform transportable tablespaces is introduced in this release.

See Also:

Oracle Database Administrator's Guide for details on transportable tablespaces

- Regular Expression Support

A set of SQL functions introduced in this release allow you to perform queries and manipulate string data stored in LOB types and other character datatypes using regular expressions.

See Also:

- Oracle Database Application Developer's Guide - Fundamentals for information on supported regular expression syntax.

- Oracle Database SQL Reference for additional details on Oracle SQL functions for regular expressions.

- Oracle Database Globalization Support Guide for details on using SQL regular expression functions in a multilingual environment.

- Mastering Regular Expressions published by O'Reilly & Associates, Inc.

- Implicit Conversion Between NCLOB and CLOB Datatypes

This release introduces support for implicit conversions between NCLOB and CLOB datatypes. You can perform operations such as cross-type assignments and parameter passing between these types without losing data or character set formatting properties.

See Also:

"Implicit Conversion Between CLOB and NCLOB Datatypes in SQL"

- Partitioned Index-Organized Tables - LOB Support

LOB columns are now supported in all types of partitioned index-organized tables.

See Also:

"LOBs in Index Organized Tables"

- LogMiner Support for More Types: LONG, Multibyte CLOB and NCLOB

LogMiner and SQL Apply now support multibyte CLOB and NCLOB data. SQL Apply now also supports LONG data. Support of additional datatypes means that you can now mine a greater variety of data.

See Also:

Oracle Data Guard Concepts and Administration

- New Column in V$TEMPORARY_LOBS

A new column named 'ABSTRACT_LOBS' has been added to the V$TEMPORARY_LOBS table. This column displays the number of abstract LOBs accumulated in the current session. Abstract LOBs are temporary lobs returned from queries involving XMLType columns. See the Oracle Database Reference for details on the V$TEMPORARY_LOBS table.

Restrictions Removed in Oracle Database 10g Release 1

The following restrictions on LOB features were removed in Oracle Database 10g Release 1:

- NCLOB as an attribute of an object type at table creation

In previous releases you could not specify an NCLOB as an attribute of an object type when creating a table. This restriction no longer applies.

- Restrictions on LOBs in index organized tables were removed. See "Restrictions for LOBs in Partitioned Index-Organized Tables" for more information.

LOB Features Introduced in Oracle9i Release 2

This section describes features introduced in Oracle9i Release 2 (9.2).

This release introduces new PL/SQL APIs with improved features for loading binary and character data from LOBs:

- DBMS_LOB.LOADBLOBFROMFILE

This API enables you to load binary large objects from operating system files into internal persistent LOBs and temporary LOBs.

See Also:

"Loading a BLOB with Data from a BFILE"

- DBMS_LOB.LOADCLOBFROMFILE

This API enables you to load character large objects from operating system files into internal persistent LOBs and temporary LOBs. This API performs the proper character set conversions from the BFILE data character set to the destination CLOB/NCLOB character set.

See Also:

"Loading a CLOB or NCLOB with Data from a BFILE"

- Parallel Execution Support for DML Operations on LOBs

See Also:

"Parallel DML Support for LOBs"

Restrictions Removed in Oracle9i Release 2

The following restrictions are removed in Oracle9i Release 2 (9.2):

- Trigger restrictions removed

This release supports DML BEFORE ROW Trigger :new for LOBs. This means that triggers on LOBs follow the same rules as triggers on any other type of column.

Prior to Release 9.2, in a PL/SQL trigger body of an BEFORE ROW DML trigger, you could read the :old value of the LOB, but you could not read the :new value.

In releases prior to 9.2, if a view with a LOB column has an INSTEAD OF TRIGGER, then you cannot specify a string INSERT/UPDATE into the LOB column. This restriction is removed in release 9.2. For example:

CREATE TABLE t(a LONG);
CREATE VIEW v AS SELECT * FROM t;
CREATE TRIGGER trig INSTEAD OF insert on v....;
ALTER TABLE t MODIFY (a CLOB);
INSERT INTO v VALUES ('abc');       /* works now */

- Locally managed tablespaces restriction removed

You can now create LOB columns in locally managed tablespaces.

- LOBs in AUTO segment-managed tablespaces restriction removed

You can now store LOBs in AUTO segment-managed tablespaces.

- NCLOB parameters

NCLOB parameters are now allowed as attributes in object types.

- Partitioned Index Organized Tables

Partitioned Index Organized Tables (PIOT) are now supported.

- Client-side PL/SQL DBMS_LOB procedures

Client-side PL/SQL DBMS_LOB procedures are now supported.

- Selecting a bind variable into a LOB column

For fetch, in prior releases, you could not use SELECT INTO to bind a character variable to a LOB column. SELECT INTO used to bind LOB locators to the column. This constraint has been removed.

LOB Features Introduced in Oracle9i Release 1

The following LOB features were introduced in Oracle9i Release 1 (9.0.1):

- Data Interface for LOBs

Using the data interface for LOBs, you can bind and define character data for CLOB columns and binary data for BLOB columns. Doing so, enables you to insert data directly into the LOB column and select data from the LOB column without using a LOB locator.

When using a version of the Oracle Database client that differs from the version of the Oracle Database server, queries produce different results when a client application selects a LOB column defining it as a character type or a LOB type. The following table outlines the characteristics of various Oracle Database client and server combinations in this release and prior to this release.

Client Release

LOB Column Defined on the Client Side As

Result Using Server from Oracle Database Release 1 (9.0.1) and higher

Result Using Server prior to Oracle Database Release 1 (9.0.1)

9.0.1 and higher

Character type

Server sends data.

Client raises error.

9.0.1 and higher

LOB type

Server sends locator.

Server sends locator.

Prior to Rel.9.0.1

Character type

Client raises error.

Client raises error.

Prior to Rel.9.0.1

LOB type

Server sends locator.

Server sends locator.

See Also:

Chapter 13, "Data Interface for Persistent LOBs"

- Using SQL Semantics with LOBs

In this release, for the first time, you can access (internal persistent) LOBs using SQL VARCHAR2 semantics, such as SQL string operators and functions. By providing you with an SQL interface, which you are familiar with, accessing LOB data can be greatly facilitated. These semantics are recommended when using small-sized LOBs (~ 10-100KB).

See Also:

Chapter 9, "SQL Semantics and LOBs"

- Using Oracle C++ Call Interface (OCCI) with LOBs

Oracle C++ Call Interface (OCCI) is a new C++ API for manipulating data in an Oracle database. OCCI is organized as an easy-to-use set of C++ classes which enable a C++ program to connect to a database, run SQL statements, insert/update values in database tables, retrieve results of a query, run stored procedures in the database, and access metadata of database schema objects. OCCI API provides advantages over JDBC and ODBC.

See Also:

Chapter 6, "Overview of Supplied LOB APIs"

- New JDBC LOB Functionality

The following are new JDBC LOB-related functionality:

- Temporary LOB APIs: create temporary LOBs and destroy temporary LOBs

- Trim APIs: trim the LOBs to the specified length

- Open and Close APIs: open and close LOBs explicitly

- New Streaming APIs: read and write LOBs as Java streams from the specified offset.

- Empty LOB instances can now be created with JDBC. The instances do not require database round trips.

- Support for LOBs in Partitioned Index-Organized Tables

Oracle9i introduces support for LOB, VARRAY columns stored as LOBs, and BFILEs in partitioned index-organized tables. Results of queries on LOB columns in these tables is similar to that of LOB columns in conventional (heap-organized) partitioned tables, except for a few minor differences.

See Also:

Chapter 5, "Advanced Design Considerations"

- Using OLEDB and LOBs (new to this manual)

OLE DB is an open specification for accessing various types of data from different stores in a uniform way. OLEDB supports the following functions for these LOB types:

- Persistent LOBs: READ/WRITE through the rowset.

- BFILEs: READ-ONLY through the rowset.

See Also:

"Oracle Provider for OLE DB (OraOLEDB)"

Restrictions Removed in Oracle9i Release 1

This section describes restrictions removed in Oracle9i Release 1 (9.0.1).

In earlier releases, you could not call functions and procedures in DBMS_LOB packages from client-side PL/SQL. This restriction is removed in release version 9.0.1. In this release, you can call DBMS_LOB functions and procedures from client-side or server-side PL/SQL.

Part I

Getting Started

This part gives an introduction to Large Objects and introduces general concepts you need to be familiar with to use LOBs in your application.

This part contains these chapters:

- Chapter 1, "Introduction to Large Objects"

- Chapter 2, "Working with LOBs"

- Chapter 3, "Managing LOBs: Database Administration"

1 Introduction to Large Objects

This chapter introduces Large Objects (LOBs) and discusses how LOB datatypes are used in application development. This chapter contains these topics:

- What Are Large Objects?

- Why Use Large Objects?

- Why Not Use LONGs?

- Different Kinds of LOBs

- Introducing LOB Locators

- Database Semantics for Internal and External LOBs

- Large Object Datatypes

- Object Datatypes and LOBs

- Storing and Creating Other Datatypes with LOBs

What Are Large Objects?

Large Objects (LOBs) are a set of datatypes that are designed to hold large amounts of data. A LOB can hold up to a maximum size ranging from 8 terabytes to 128 terabytes depending on how your database is configured. Storing data in LOBs enables you to access and manipulate the data efficiently in your application.

Why Use Large Objects?

This section introduces different types of data that you encounter when developing applications and discusses which kinds of data are suitable for large objects.

In the world today, applications must deal with the following kinds of data:

- Simple structured data.

This data can be organized into simple tables that are structured based on business rules.

- Complex structured data

This kind of data is complex in nature and is suited for the object-relational features of the Oracle database such as collections, references, and user-defined types.

- Semi-structured data

This kind of data has a logical structure that is not typically interpreted by the database. For example, an XML document that is processed by your application or an external service, can be thought of as semi-structured data. The database provides technologies such as Oracle XML DB, Advanced Queueing, and Messages to help your application work with semi-structured data.

- Unstructured data

This kind of data is not broken down into smaller logical structures and is not typically interpreted by the database or your application. A photographic image stored as a binary file is an example of unstructured data.

Large objects are suitable for these last two kinds of data: semi-structured data and unstructured data. Large objects features allow you to store these kinds of data in the database as well as in operating system files that are accessed from the database.

With the growth of the internet and content-rich applications, it has become imperative that the database support a datatype that:

- Can store unstructured and semi-structured data in an efficient manner.

- Is optimized for large amounts of data.

- Provides a uniform way of accessing data stored within the database or outside the database.

Using LOBs for Semi-structured Data

Examples of semi-structured data include document files such as XML documents or word processor files. These kinds of documents contain data in a logical structure that is processed or interpreted by an application, and is not broken down into smaller logical units when stored in the database.

Applications involving semi-structured data typically use large amounts of character data. The Character Large Object (CLOB) and National Character Large Object (NCLOB) datatypes are ideal for storing and manipulating this kind of data.

Binary File objects (BFILE datatypes) can also store character data. You can use BFILEs to load read-only data from operating system files into CLOB or NCLOB instances that you then manipulate in your application.

Using LOBs for Unstructured Data

Unstructured data cannot be decomposed into standard components. For example, data about an employee can be structured into a name, which is stored as a string; an identifier, such as an ID number, a salary and so on. A photograph, on the other hand, consists of a long stream of 1s and 0s. These bits are used to switch pixels on or off so that you can see the picture on a display, but are not broken down into any finer structure for database storage.

Also, unstructured data such as text, graphic images, still video clips, full motion video, and sound waveforms tends to be large in size. A typical employee record may be a few hundred bytes, while even small amounts of multimedia data can be thousands of times larger.

SQL datatypes that are ideal for large amounts of unstructured binary data include the BLOB datatype (Binary Large Object) and the BFILE datatype (Binary File object).

Why Not Use LONGs?

The database supports LONG as well as LOB datatypes. When possible, change your existing applications to use LOBs instead of LONGs because of the added benefits that LOBs provide. LONG-to-LOB migration enables you to easily migrate your existing applications that access LONG columns, to use LOB columns.

See Also:

Chapter 11, "Migrating Columns from LONGs to LOBs"

Applications developed for use with Oracle Database version 7 and earlier, used the LONG or LONG RAW data type to store large amounts of unstructured data.

With the Oracle8i and later versions of the database, using LOB datatypes is recommended for storing large amounts of structured and semi-structured data. LOB datatypes have several advantages over LONG and LONG RAW types including:

- LOB Capacity: LOBs can store much larger amounts of data. LOBs can store 4GB of data or more depending on you system configuration. LONG and LONG RAW types are limited to 2GB of data.

- Number of LOB columns in a table: A table can have multiple LOB columns. LOB columns in a table can be of any LOB type. In Oracle Database Release 7.3 and higher, tables are limited to a single LONG or LONG RAW column.

- Random piece-wise access: LOBs support random access to data, but LONGs support only sequential access.

- LOBs can also be object attributes.

Different Kinds of LOBs

Different kinds of LOBs can be stored in the database or in external files.

Note:

LOBs in the database are sometimes also referred to as internal LOBs or internal persistent LOBs.

Internal LOBs

LOBs in the database are stored inside database tablespaces in a way that optimizes space and provides efficient access. The following SQL datatypes are supported for declaring internal LOBs: BLOB, CLOB, and NCLOB. Details on these datatypes are given in "Large Object Datatypes".

Persistent and Temporary LOBs

Internal LOBs (LOBs in the database) can be either persistent or temporary. A persistent LOB is a LOB instance that exists in a table row in the database. A temporary LOB instance is created when you instantiate a LOB only within the scope of your local application.

A temporary instance becomes a persistent instance when you insert the instance into a table row.

Persistent LOBs use copy semantics and participate in database transactions. You can recover persistent LOBs in the event of transaction or media failure, and any changes to a persistent LOB value can be committed or rolled back. In other words, all the Atomicity Consistency Isolation Durability (ACID) properties that pertain to using database objects pertain to using persistent LOBs.

External LOBs and the BFILE Datatype

External LOBs are data objects stored in operating system files, outside the database tablespaces. The database accesses external LOBs using the SQL datatype BFILE. The BFILE datatype is the only external LOB datatype.

BFILEs are read-only datatypes. The database allows read-only byte stream access to data stored in BFILEs. You cannot write to a BFILE from within your application.

The database uses reference semantics with BFILE columns. Data stored in a table column of type BFILE, is physically located in an operating system file, not in the database tablespace.

You typically use BFILEs to hold:

- Binary data that does not change while your application is running, such as graphics.

- Data that is loaded into other large object types, such as a BLOB or CLOB where the data can then be manipulated.

- Data that is appropriate for byte-stream access, such as multimedia.

- Read-only data that is relatively large in size, to avoid taking up large amounts database tablespace.

Any storage device accessed by your operating system can hold BFILE data, including hard disk drives, CD-ROMs, PhotoCDs and DVDs. The database can access BFILEs provided the operating system supports stream-mode access to the operating system files.

Note:

External LOBs do not participate in transactions. Any support for integrity and durability must be provided by the underlying file system as governed by the operating system.

Introducing LOB Locators

A LOB instance has a locator and a value. The LOB locator is a reference to where the LOB value is physically stored. The LOB value is the data stored in the LOB.

When you use a LOB in an operation such as passing a LOB as a parameter, you are actually passing a LOB locator. For the most part, you can work with a LOB instance in your application without being concerned with the semantics of LOB locators. There is no need to dereference LOB locators, as is required with pointers in some programming languages.

There are some issues regarding the semantics of LOB locators and how LOB values are stored that you should be aware of. These details are covered in the context of the discussion where they apply throughout this guide.

See Also:

- "LOB Locator and LOB Value"

- "LOB Locators and BFILE Locators"

- "LOB Storage"

Database Semantics for Internal and External LOBs

In all programmatic environments, database semantics differ between internal LOBs and external LOBs as follows:

- Internal LOBs use copy semantics.

With copy semantics, both the LOB locator and LOB value are logically copied during insert, update, or assignment operations. This ensures that each table cell or each variable containing a LOB, holds a unique LOB instance.

- External LOBs use reference semantics.

With reference semantics, only the LOB locator is copied during insert operations. (Note that update operations do not apply to external LOBs as external LOBs are read-only. This is explained in more detail later in this section.)

Large Object Datatypes

Table 1-1 describes each large object datatype supported by the database and describes the kind of data each datatype is typically used for. The names of datatypes given here are the SQL datatypes provided by the database. In general, the descriptions given for the datatypes in this table and the rest of this book also apply to the corresponding datatypes provided for other programmatic environments. Also, note that the term "LOB" is generally used to refer to the set of all large object datatypes.

Table 1-1 Large Object Datatypes

SQL Datatype

Description

BLOB

Binary Large Object
Stores any kind of data in binary format. Typically used for multimedia data such as images, audio, and video.

CLOB

Character Large Object
Stores string data in the database character set format. Used for large strings or documents that use the database character set exclusively. Characters in the database character set are in a fixed width format.

NCLOB

National Character Set Large Object
Stores string data in National Character Set format. Used for large strings or documents in the National Character Set. Supports characters of varying width format.

BFILE

External Binary File
A binary file stored outside of the database in the host operating system file system, but accessible from database tables. BFILEs can be accessed from your application on a read-only basis. Use BFILEs to store static data, such as image data, that does not need to be manipulated in applications.

Any kind of data, that is, any operating system file, can be stored in a BFILE. For example, you can store character data in a BFILE and then load the BFILE data into a CLOB specifying the character set upon loading.

Object Datatypes and LOBs

You can declare LOB datatypes as fields, or members, of object datatypes. For example, you can have an attribute of type CLOB on an object type. In general, there is no difference in the usage of a LOB instance in a LOB column and the usage of a LOB instance that is a member or of an object datatype. Any difference in usage is called out when it applies. When used in this guide, the term LOB attribute refers to a LOB instance that is a member of an object datatype. Unless otherwise specified, discussions that apply to LOB columns also apply to LOB attributes.

Storing and Creating Other Datatypes with LOBs

You can use LOBs to create other user-defined datatypes or store other datatypes as LOBs. This section discusses some of the datatypes provided with the database as examples of datatypes that are stored or created with LOB types.

VARRAYs Stored as LOBs

An instance of type VARRAY in the database is stored as an array of LOBs when you create a table in the following scenarios:

- If the VARRAY storage clause— VARRAY varray_item STORE AS —is not specified, and the declared size of varray data is more than 4000 bytes.

- If the varray column properties are specified using the STORE AS LOB clause— VARRAY varray_item STORE AS LOB ...

XMLType Columns Stored as CLOBs

A good example of how LOB datatypes can be used to store other datatypes is the XMLType datatype. The XMLType datatype is stored as a CLOB type. Setting up your table or column to store XMLType datatypes as CLOBs enables you to store schema-less XML documents in the database.

See Also:

- Oracle XML DB Developer's Guide for information on creating XMLType tables and columns and how XML is stored in CLOBs.

- Oracle XML Developer's Kit Programmer's Guide, for information about working with XML.

LOBs Used in Oracle interMedia

Oracle interMedia uses LOB datatypes to create datatypes specialized for use in multimedia application such as interMedia ORDAudio, ORDDoc, ORDImage, and ORDVideo. Oracle interMedia uses the database infrastructure to define object types, methods, and LOBs necessary to represent these specialized types of data in the database.

See Also:

- Oracle interMedia User's Guide for more information on using interMedia.

- Oracle interMedia Reference for more information on using interMedia datatypes.

2 Working with LOBs

This chapter describes the usage and semantics of LOBs that you need to be familiar with to use LOBs in your application. Various techniques for working with LOBs are covered.

Most of the discussions in this chapter regarding persistent LOBs assume that you are dealing with LOBs in tables that already exist. The task of creating tables with LOB columns is typically performed by your database administrator. See Chapter 4, "LOBs in Tables" of this guide for details on creating tables with LOB columns.

This chapter contains these topics:

- LOB Column States

- Locking a Row Containing a LOB

- Opening and Closing LOBs

- LOB Locator and LOB Value

- LOB Locators and BFILE Locators

- Accessing LOBs

- LOB Rules and Restrictions

LOB Column States

The techniques you use when accessing a cell in a LOB column differ depending on the state of the given cell. A cell in a LOB Column can be in one of the following states:

- NULL

The table cell is created, but the cell holds no locator or value.

- Empty

A LOB instance with a locator exists in the cell, but it has no value. The length of the LOB is zero.

- Populated

A LOB instance with a locator and a value exists in the cell.

Locking a Row Containing a LOB

You can lock a row containing a LOB to prevent other database users from writing to the LOB during a transaction. To lock a row containing a LOB, specify the FOR UPDATE clause when you select the row. While the row is locked, other users cannot lock or update the LOB, until you end your transaction.

Opening and Closing LOBs

The LOB APIs include operations that enable you to explicitly open and close a LOB instance. You can open and close a persistent LOB instance of any type: BLOB, CLOB, NCLOB, or BFILE. You open a LOB to achieve one or both of the following results:

- Open the LOB in read-only mode.

This ensures that the LOB (both the LOB locator and LOB value) cannot be changed in your session until you explicitly close the LOB. For example, you can open the LOB to ensure that the LOB is not changed by some other part of your program while you are using the LOB in a critical operation. After you perform the operation, you can then close the LOB.

- Open the LOB in read write/mode—persistent BLOB, CLOB, or NCLOB instances only.

Opening a LOB in read write mode defers any index maintenance on the LOB column until you close the LOB. Opening a LOB in read write mode is only useful if there is an extensible index on the LOB column and you do not want the database to perform index maintenance every time you write to the LOB. This technique can increase the performance of your application if you are doing several write operations on the LOB while it is open.

If you open a LOB, then you must close the LOB at some point later in your session. This is the only requirement for an open LOB. While a LOB instance is open, you can perform as many operations as you want on the LOB—provided the operations are allowed in the given mode.

See Also:

"Opening Persistent LOBs with the OPEN and CLOSE Interfaces" for details on usage of these APIs.

LOB Locator and LOB Value

There are two techniques that you can use to access and modify LOB values:

- Using the Data Interface for LOBs

- Using the LOB Locator to Access and Modify LOB Values

Using the Data Interface for LOBs

You can perform bind and define operations on CLOB and BLOB columns in C applications using the data interface for LOBs in OCI. Doing so, enables you to insert or select out data in a LOB column without using a LOB locator as follows:

- Using a bind variable associated with a LOB column to insert character data into a CLOB, or RAW data into a BLOB.

- Using a define operation to define an output buffer in your application that will hold character data selected from a CLOB, or RAW data selected from a BLOB.

See Also:

Chapter 13, "Data Interface for Persistent LOBs" for more information on implicit assignment of LOBs to other datatypes.

Using the LOB Locator to Access and Modify LOB Values

The value of a LOB instance stored in the database can be accessed through a LOB locator, a reference to the location of the LOB value. Database tables store only locators in CLOB, BLOB, NCLOB and BFILE columns. Note the following with respect to LOB locators and values:

- To access or manipulate a LOB value, you pass the LOB locator to the various LOB APIs.

- A LOB locator can be assigned to any LOB instance of the same type.

- The characteristics of a LOB as being temporary or persistent have nothing to do with the locator. The characteristics of temporary or persistent apply only to the LOB instance.

LOB Locators and BFILE Locators

There are differences between the semantics of locators for LOB types BLOB, CLOB, and NCLOB on one hand, and the semantics of locators for the BFILE type on the other hand:

- For LOB types BLOB, CLOB, and NCLOB, the LOB column stores a locator to the LOB value. Each LOB instance has its own distinct LOB locator and also a distinct copy of the LOB value.

- For initialized BFILE columns, the row stores a locator to the external operating system file that holds the value of the BFILE. Each BFILE instance in a given row has its own distinct locator; however, two different rows can contain a BFILE locator that points to the same operating system file.

Regardless of where the value of a LOB is stored, a locator is stored in the table row of any initialized LOB column. Note that when the term locator is used without an identifying prefix term, it refers to both LOB locators and BFILE locators. Also, when you select a LOB from a table, the LOB returned is always a temporary LOB. For more information on working with locators for temporary LOBs, see "LOBs Returned from SQL Functions".

Table print_media

The table print_media of the Oracle Database Sample Schema PM, is used in many examples in this documentation and is defined as:

CREATE TABLE print_media
( product_id        NUMBER(6)
, ad_id             NUMBER(6)
, ad_composite      BLOB
, ad_sourcetext     CLOB
, ad_finaltext      CLOB
, ad_fltextn        NCLOB
, ad_textdocs_ntab  textdoc_tab
, ad_photo          BLOB
, ad_graphic        BFILE
, ad_header         adheader_typ
) NESTED TABLE ad_textdocs_ntab STORE AS textdocs_nestedtab;

See Also:

"Creating a Table Containing One or More LOB Columns" for the details of how print_media and its associated tables and files are created.

Initializing a LOB Column to Contain a Locator

Any LOB instance that is NULL does not have a locator. Before you can pass a LOB instance to any LOB API routine, the instance must contain a locator. For example, you can select a NULL LOB from a row, but you cannot pass the instance to the PL/SQL DBMS_LOB.READ procedure. The following sub-sections describe how to initialize a persistent LOB column and how to initialize a BFILE column.

Initializing a Persistent LOB Column

Before you can start writing data to a persistent LOB using the supported programmatic environment interfaces (PL/SQL, OCI, OCCI, Pro*C/C++, Pro*COBOL, Visual Basic, Java, or OLEDB), the LOB column/attribute must be made non-NULL, that is, it must contain a locator.

You can accomplish this by initializing the persistent LOB to empty in an INSERT/UPDATE statement using the functions EMPTY_BLOB for BLOBs or EMPTY_CLOB for CLOBs and NCLOBs.

Note:

You can use SQL to populate a LOB column with data even if it contains a NULL value.

See Also:

Chapter 4, "LOBs in Tables" for more information on initializing LOB columns.

Running the EMPTY_BLOB() or EMPTY_CLOB() function in and of itself does not raise an exception. However, using a LOB locator that was set to empty to access or manipulate the LOB value in any PL/SQL DBMS_LOB or OCI function will raise an exception.

Valid places where empty LOB locators may be used include the VALUES clause of an INSERT statement and the SET clause of an UPDATE statement.

See Also:

- "Directory Objects" for details of CREATE DIRECTORY and BFILENAME usage

- CREATE DIRECTORY statement in Oracle Database Reference. for more information about creating a directory object

- Oracle Database SQL Reference, CREATE DIRECTORY statement

Note:

Character strings are inserted using the default character set for the instance.

The following INSERT statement in the PM, table print_media:

- Populates ad_sourcetext with the character string 'my Oracle',

- Sets ad_composite, ad_finaltext, and ad_fltextn to an empty value,

- Sets ad_photo to NULL, and

- Initializes ad_graphic to point to the file my_picture located under the logical directory my_directory_object.

CREATE OR REPLACE DIRECTORY my_directory_object AS 'oracle/work/tklocal';
INSERT INTO print_media VALUES (1726, 1, EMPTY_BLOB(),
'my Oracle', EMPTY_CLOB(), EMPTY_CLOB(),
NULL, NULL, BFILENAME('my_directory_object', 'my_picture'), NULL);

Similarly, the LOB attributes for the ad_header column in print_media can be initialized to NULL, empty, or a character/raw literal, which is shown in the following statement:

INSERT INTO print_media (product_id, ad_id, ad_header)
VALUES (1726, 1, adheader_typ('AD FOR ORACLE', sysdate,
'Have Grid', EMPTY_BLOB()));

See Also:

- "Inserting a Row by Selecting a LOB From Another Table"

- "Inserting a LOB Value Into a Table"

- "Inserting a Row by Initializing a LOB Locator Bind Variable"

- "OCILobLocator Pointer Assignment" for details on LOB locator semantics in OCI

Initializing BFILEs

Before you can access BFILE values using LOB APIs, the BFILE column or attribute must be made non-NULL. You can initialize the BFILE column to point to an external operating system file by using the BFILENAME function.

See Also:

"Accessing BFILEs" for more information on initializing BFILE columns.

Accessing LOBs

You can access a LOB instance using the following techniques:

- Accessing a LOB Using SQL

- Accessing a LOB Using the Data Interface

- Accessing a LOB Using the Locator Interface

Accessing a LOB Using SQL

Support for columns that use LOB datatypes is built into many SQL functions. This support enables you to use SQL semantics to access LOB columns in SQL. In most cases, you can use the same SQL semantics on a LOB column that you would use on a VARCHAR2 column.

See Also:

For details on SQL semantics support for LOBs, see Chapter 9, "SQL Semantics and LOBs".

Accessing a LOB Using the Data Interface

You can select a LOB directly into CHAR or RAW buffers using the LONG-to-LOB API in OCI and PL/SQL. In the following PL/SQL example, ad_finaltext is selected into a VARCHAR2 buffer final_ad.

DECLARE
final_ad VARCHAR(32767);
BEGIN
SELECT ad_finaltext INTO final_ad FROM print_media
WHERE product_id = 2056 and ad_id = 12001 ;
/* PUT_LINE can only output up to 255 characters at a time  */
...
DBMS_OUTPUT.PUT_LINE(final_ad);
/* more calls to read final_ad */
...
END;

See Also:

For more details on accessing LOBs using the data interface, see Chapter 13, "Data Interface for Persistent LOBs".

Accessing a LOB Using the Locator Interface

You can access and manipulate a LOB instance by passing the LOB locator to the LOB APIs supplied with the database. An extensive set of LOB APIs is provided with each supported programmatic environment. In OCI, a LOB locator is mapped to a locator pointer which is used to access the LOB value.

Note:

In all environments, including OCI, the LOB APIs operate on the LOB value implicitly—there is no need to "dereference" the LOB locator.

See Also:

- Chapter 6, "Overview of Supplied LOB APIs"

- "OCILobLocator Pointer Assignment" for details on LOB locator semantics in OCI

LOB Rules and Restrictions

This section provides details on LOB rules and restrictions.

Rules for LOB Columns

LOB columns are subject to the following rules and restrictions:

- You cannot specify a LOB as a primary key column.

- Oracle Database has limited support for remote LOBs. You can perform create table as select and insert/update as select of LOB columns.

For example:

CREATE TABLE t AS SELECT * FROM table1@remote_site;
INSERT INTO t SELECT * FROM table1@remote_site;
UPDATE t SET lobcol = (SELECT lobcol FROM table1@remote_site);
INSERT INTO table1@remote_site SELECT * from local_table;
UPDATE table1@remote_site SET lobcol = (SELECT lobcol FROM local_table);
DELETE FROM table1@remote_site <WHERE clause involving non_lob_columns>

In statements structured like the preceding examples, only standalone LOB columns are allowed in the select list.

SQL functions and DBMS_LOB APIs are not supported for use with remote LOB columns. For example, the following statement is supported:

CREATE TABLE AS SELECT clob_col FROM tab@dbs2;

However, the following statement is not supported:

CREATE TABLE AS SELECT DBMS_LOB.SUBSTR(clob_col) from tab@dbs2;

In addition, you can insert a character or binary buffer into a remote CLOB or BLOB, and select a remote CLOB or BLOB into a character or binary buffer. For example (in PL/SQL):

SELECT clobcol1, type1.blobattr INTO varchar_buf1, raw_buf2 FROM
table1@remote_site;
INSERT INTO table1@remotesite (clobcol1, type1.blobattr) VALUES varchar_buf1,
raw_buf2;

This is the only supported syntax involving LOBs in remote tables. No other usage is supported.

- Clusters cannot contain LOBs, either as key or nonkey columns.

- The following data structures are supported only as temporary instances. You cannot store these instances in database tables:

- VARRAY of any LOB type

- VARRAY of any type containing a LOB type, such as an object type with a LOB attribute

- ANYDATA of any LOB type

- ANYDATA of any type containing a LOB

- You cannot specify LOB columns in the ORDER BY clause of a query, or in the GROUP BY clause of a query or in an aggregate function.

- You cannot specify a LOB column in a SELECT... DISTINCT or SELECT... UNIQUE statement or in a join. However, you can specify a LOB attribute of an object type column in a SELECT... DISTINCT statement or in a query that uses the UNION or MINUS set operator if the column's object type has a MAP or ORDER function defined on it.

- You cannot specify LOB columns in ANALYZE... COMPUTE or ANALYZE... ESTIMATE statements.

- The first (INITIAL) extent of a LOB segment must contain at least three database blocks.

- When creating an UPDATE DML trigger, you cannot specify a LOB column in the UPDATE OF clause.

- You cannot specify a LOB column as part of an index key. However, you can specify a LOB column in the indextype specification of a domain index. In addition, Oracle Text lets you define an index on a CLOB column.

- In an INSERT... AS SELECT operation, you can bind up to 4000 bytes of data to LOB columns and attributes.

- If a table has both LONG and LOB columns, you cannot bind more than 4000 bytes of data to both the LONG and LOB columns in the same SQL statement. However, you can bind more than 4000 bytes of data to either the LONG or the LOB column.

Note:

For a table on which you have defined a DML trigger, if you use OCI functions or DBMS_LOB package to change the value of a LOB column or the LOB attribute of an object type column, the database does not fire the DML trigger.

See Also:

- "Restrictions Removed in Oracle Database 10g Release 2"

- "Restrictions Removed in Oracle Database 10g Release 1"

- "RestrictionsRemoved in Oracle9i Release 2"

- "Restrictions for LOBs in Partitioned Index-Organized Tables"

- Chapter 11, "Migrating Columns from LONGs to LOBs" under "Migrating Applications from LONGs to LOBs", describes LONG to LOB migration limitations for clustered tables, replication, triggers, domain indexes, and function-based indexes.

- "Unsupported Use of LOBs in SQL" for restrictions on SQL semantics.

- For details on the INITIAL extent of a LOB segment, see "Restriction on First Extent of a LOB Segment" .

- LOBs in partitioned index-organized tables are also subject to a number of other restrictions. See "Restrictions for LOBs in Partitioned Index-Organized Tables" for more information.

Restrictions for LOB Operations

Other general LOB restrictions include the following:

- In SQL Loader, A field read from a LOBFILE cannot be used as an argument to a clause. See "Database Utilities for Loading Data into LOBs" for more information.

- Session migration is not supported for BFILEs in shared server (multithreaded server) mode. This implies that operations on open BFILEs can persist beyond the end of a call to a shared server. In shared server sessions, BFILE operations will be bound to one shared server, they cannot migrate from one server to another.

3 Managing LOBs: Database Administration

This chapter describes administrative tasks that must be performed to set up, maintain, and use a database that contains LOBs.

This chapter contains these topics:

- Database Utilities for Loading Data into LOBs

- Managing Temporary LOBs

- Managing BFILEs

- Changing Tablespace Storage for a LOB

Database Utilities for Loading Data into LOBs

The following utilities are recommended for bulk loading data into LOB columns as part of database setup or maintenance tasks:

- SQL*Loader

- Oracle DataPump

Note:

Application Developers: If you are loading data into a LOB in your application, then using the LOB APIs is recommended. See Chapter 14, " LOB APIs for Basic Operations" for details on APIs that allow you to load LOBs from files.

Using SQL*Loader to Load LOBs

There are two general techniques for using SQL*Loader to load data into LOBs:

- Loading data from a primary data file

- Loading from a secondary data file using LOBFILEs

Consider the following issues when loading LOBs with SQL*Loader:

- For SQL*Loader conventional path loads, failure to load a particular LOB does not result in the rejection of the record containing that LOB; instead, the record ends up containing an empty LOB.

For SQL*Loader direct-path loads, the LOB could be empty or truncated. LOBs are sent in pieces to the server for loading. If there is an error, then the LOB piece with the error is discarded and the rest of that LOB is not loaded. In other words, if the entire LOB with the error is contained in the first piece, then that LOB column will either be empty or truncated.

- When loading from LOBFILEs specify the maximum length of the field corresponding to a LOB-type column. If the maximum length is specified, then it is taken as a hint to help optimize memory usage. It is important that the maximum length specification does not underestimate the true maximum length.

- When using SQL*Loader direct-path load, loading LOBs can take up substantial memory. If the message "SQL*Loader 700 (out of memory)" appears when loading LOBs, then internal code is probably batching up more rows in each load call than can be supported by your operating system and process memory. A work-around is to use the ROWS option to read a smaller number of rows in each data save.

- You can also use the Direct Path API to load LOBs.

- Using LOBFILEs is recommended when loading columns containing XML data in CLOBs or XMLType columns. Whether you perform a direct-path load or a conventional path load with SQL*Loader depends on whether you need to validate XML documents upon loading.

- If the XML document must be validated upon loading, then use conventional path load.

- If it is not necessary to ensure that the XML document is valid or you can safely assume that the XML document is valid, then you can perform a direct-path load. Performance is higher when you use direct-path load because the overhead of XML validation is incurred.

A conventional path load executes SQL INSERT statements to populate tables in an Oracle database. A direct path load eliminates much of the Oracle database overhead by formatting Oracle data blocks and writing the data blocks directly to the database files.

A direct-path load does not compete with other users for database resources, so it can usually load data at near disk speed. Considerations inherent to direct path loads, such as restrictions, security, and backup implications, are discussed in Oracle Database Utilities.

- Tables to be loaded must already exist in the database. SQL*Loader never creates tables. It loads existing tables that either already contain data or are empty.

- The following privileges are required for a load:

- You must have INSERT privileges on the table to be loaded.

- You must have DELETE privilege on the table to be loaded, when using the REPLACE or TRUNCATE option to empty out the old data before loading the new data in its place.

See Also:

For details on using SQL*Loader to load LOBs and other details on SQL*Loader usage, refer to the Oracle Database Utilities guide.

Using SQL*Loader to Populate a BFILE Column

This section describes how to load data from files in the file system into a BFILE column.

See Also:

"Supported Environments for BFILE APIs"

Note that the BFILE datatype stores unstructured binary data in operating system files outside the database. A BFILE column or attribute stores a file locator that points to a server-side external file containing the data.

Note:

A particular file to be loaded as a BFILE does not have to actually exist at the time of loading.

SQL*Loader assumes that the necessary DIRECTORY objects have already been created.

See Also:

See "Directory Objects" and the sections following it for more information on creating directory objects.

A control file field corresponding to a BFILE column consists of column name followed by the BFILE directive.

The BFILE directive takes as arguments a DIRECTORY object name followed by a BFILE name. Both of these can be provided as string constants, or they can be dynamically sourced through some other field.

See Also:

Oracle Database Utilities for details on SQL*Loader syntax.

The following two examples illustrate the loading of BFILES.

Note:

You may need to set up the following data structures for certain examples to work:

CONNECT system/manager
GRANT CREATE ANY DIRECTORY to samp;
CONNECT samp/samp
CREATE OR REPLACE DIRECTORY adgraphic_photo as '/tmp';
CREATE OR REPLACE DIRECTORY adgraphic_dir as '/tmp';

In the following example only the file name is specified dynamically.

Control file:

LOAD DATA
INFILE sample9.dat
INTO TABLE Print_media
FIELDS TERMINATED BY ','
(product_id  INTEGER EXTERNAL(6),
FileName    FILLER CHAR(30),
ad_graphic  BFILE(CONSTANT "modem_graphic_2268_21001", FileName))

Data file:

007, modem_2268.jpg,
008, monitor_3060.jpg,
009, keyboard_2056.jpg,

Note:

product_ID defaults to (255) if a size is not specified. It is mapped to the file names in the data file. ADGRAPHIC_PHOTO is the directory where all files are stored. ADGRAPHIC_DIR is a DIRECTORY object created previously.

In the following example, the BFILE and the DIRECTORY object are specified dynamically.

Control file:

LOAD DATA
INFILE sample10.dat
INTO TABLE Print_media
FIELDS TERMINATED BY ','
(
product_id INTEGER EXTERNAL(6),
ad_graphic BFILE (DirName, FileName),
FileName  FILLER CHAR(30),
DirName   FILLER CHAR(30)
)

Data file:

007,monitor_3060.jpg,ADGRAPHIC_PHOTO,
008,modem_2268.jpg,ADGRAPHIC_PHOTO,
009,keyboard_2056.jpg,ADGRAPHIC_DIR,

Note:

DirName FILLER CHAR (30) is mapped to the data file field containing the directory name corresponding to the file being loaded.

Using Oracle DataPump to Transfer LOB Data

You can use Oracle DataPump to transfer LOB data from one database to another.

See Also:

For details on using Oracle DataPump, refer to the Oracle Database Utilities guide.

Managing Temporary LOBs

The database keeps track of temporary LOBs in each session, and provides a v$ view called v$temporary_lobs. From the session, the application can determine which user owns the temporary LOB. As a database administrator, you can use this view to monitor and guide any emergency cleanup of temporary space used by temporary LOBs.

Managing Temporary Tablespace for Temporary LOBs

Temporary tablespace is used to store temporary LOB data. As a database administrator you control data storage resources for temporary LOB data by controlling user access to temporary tablespaces and by the creation of different temporary tablespaces.

See Also:

Refer to the Oracle Database Administrator's Guide for details on managing temporary tablespaces.

Managing BFILEs

This section describes administrative tasks for managing databases that contain BFILEs.

Rules for Using Directory Objects and BFILEs

When creating a directory object or BFILEs, ensure that the following conditions are met:

- The operating system file must not be a symbolic or hard link.

- The operating system directory path named in the Oracle DIRECTORY object must be an existing operating system directory path.

- The operating system directory path named in the Oracle DIRECTORY object should not contain any symbolic links in its components.

Setting Maximum Number of Open BFILEs

A limited number of BFILEs can be open simultaneously in each session. The initialization parameter, SESSION_MAX_OPEN_FILES defines an upper limit on the number of simultaneously open files in a session.

The default value for this parameter is 10. That is, you can open a maximum of 10 files at the same time in each session if the default value is used. If you want to alter this limit, then the database administrator can change the value of this parameter in the init.ora file. For example:

SESSION_MAX_OPEN_FILES=20

If the number of unclosed files reaches the SESSION_MAX_OPEN_FILES value, then you will not be able to open any more files in the session. To close all open files, use the DBMS_LOB.FILECLOSEALL call.

Changing Tablespace Storage for a LOB

As the database administrator, you can use the following techniques to change the default storage for a LOB after the table has been created:

- Using ALTER TABLE... MODIFY: You can change LOB tablespace storage as follows:

Note:

- The ALTER TABLE syntax for modifying an existing LOB column uses the MODIFY LOB clause, not the LOB...STORE AS clause. The LOB...STORE AS clause is only for newly added LOB columns.

- There are two kinds of LOB storage clauses: LOB_storage_clause and modify_LOB_storage_clause. In the ALTER TABLE MODIFY LOB statement, you can only specify the modify_LOB_storage_clause.

ALTER TABLE test MODIFY
LOB (lob1)
STORAGE  (
NEXT         4M
MAXEXTENTS   100
PCTINCREASE  50
)

- Using ALTER TABLE... MOVE: You can also use the MOVE clause of the ALTER TABLE statement to change LOB tablespace storage. For example:

ALTER TABLE test MOVE
TABLESPACE tbs1
LOB (lob1, lob2)
STORE AS (
TABLESPACE tbs2
DISABLE STORAGE IN ROW);

Part II

Application Design

This part covers issues that you need to consider when designing applications that use LOBs.

This part contains these chapters:

- Chapter 4, "LOBs in Tables"

- Chapter 5, "Advanced Design Considerations"

- Chapter 6, "Overview of Supplied LOB APIs"

- Chapter 7, "Performance Guidelines"

4 LOBs in Tables

This chapter describes issues specific to tables that contain LOB columns. This chapter contains these topics:

- Creating Tables That Contain LOBs

- Choosing a LOB Column Datatype

- Selecting a Table Architecture

- LOB Storage

- Indexing LOB Columns

- Manipulating LOBs in Partitioned Tables

- LOBs in Index Organized Tables

- Updating LOBs in Nested Tables

Creating Tables That Contain LOBs

When creating tables that contain LOBs, use the guidelines described in the following sections:

- Initializing Persistent LOBs to NULL or Empty

- Initializing Persistent LOB Columns and Attributes to a Value

- Initializing BFILEs to NULL or a File Name

- LOB Storage, "Defining Tablespace and Storage Characteristics for Persistent LOBs"

Initializing Persistent LOBs to NULL or Empty

You can set a persistent LOB — that is, a LOB column in a table, or a LOB attribute in an object type that you defined— to be NULL or empty:

- Setting a Persistent LOB to NULL: A LOB set to NULL has no locator. A NULL value is stored in the row in the table, not a locator. This is the same process as for all other datatypes.

- Setting a Persistent LOB to Empty: By contrast, an empty LOB stored in a table is a LOB of zero length that has a locator. So, if you SELECT from an empty LOB column or attribute, then you get back a locator which you can use to populate the LOB with data using supported programmatic environments, such as OCI or PL/SQL(DBMS_LOB). See Chapter 6, "Overview of Supplied LOB APIs" for more information on supported environments.

Details for these options are given in the following discussions.

Setting a Persistent LOB to NULL

You may want to set a persistent LOB value to NULL upon inserting the row in cases where you do not have the LOB data at the time of the INSERT or if you want to use a SELECT statement, such as the following, to determine whether the LOB holds a NULL value:

SELECT COUNT (*) FROM print_media WHERE ad_graphic IS NOT NULL;

SELECT COUNT (*) FROM print_media WHERE ad_graphic IS NULL;

Note that you cannot call OCI or DBMS_LOB functions on a NULL LOB, so you must then use an SQL UPDATE statement to reset the LOB column to a non-NULL (or empty) value.

The point is that you cannot make a function call from the supported programmatic environments on a LOB that is NULL. These functions only work with a locator, and if the LOB column is NULL, then there is no locator in the row.

Setting a Persistent LOB to Empty

You can initialize a persistent LOB to EMPTY rather that NULL. Doing so, enables you to obtain a locator for the LOB instance without populating the LOB with data. To set a persistent LOB to EMPTY, use the SQL function EMPTY_BLOB() or EMPTY_CLOB() in the INSERT statement:

INSERT INTO a_table VALUES (EMPTY_BLOB());

As an alternative, you can use the RETURNING clause to obtain the LOB locator in one operation rather than calling a subsequent SELECT statement:

DECLARE
Lob_loc  BLOB;
BEGIN
INSERT INTO a_table VALUES (EMPTY_BLOB()) RETURNING blob_col INTO Lob_loc;
/* Now use the locator Lob_loc to populate the BLOB with data */
END;

Initializing LOBs

You can initialize the LOBs in print_media by using the following INSERT statement:

INSERT INTO print_media VALUES (1001, EMPTY_CLOB(), EMPTY_CLOB(), NULL,
EMPTY_BLOB(), EMPTY_BLOB(), NULL, NULL, NULL, NULL);

This sets the value of ad_sourcetext, ad_fltextn, ad_composite, and ad_photo to an empty value, and sets ad_graphic to NULL.

Initializing Persistent LOB Columns and Attributes to a Value

You can initialize the LOB column or LOB attributes to a value that contains more than 4G bytes of data, the limit before release 10.2.

See Also:

Chapter 13, "Data Interface for Persistent LOBs"

Initializing BFILEs to NULL or a File Name

A BFILE can be initialized to NULL or to a filename. To do so, you can use the BFILENAME() function.

See Also:

"BFILENAME and Initialization".

Restriction on First Extent of a LOB Segment

The first extent of any segment requires at least 2 blocks (if FREELIST GROUPS was 0). That is, the initial extent size of the segment should be at least 2 blocks. LOBs segments are different because they need at least 3 blocks in the first extent. If you try to create a LOB segment in a permanent dictionary managed tablespace with initial = 2 blocks, then it will still work because it is possible for segments in permanent dictionary managed tablespaces to override the default storage setting of the tablespaces.

But if uniform locally managed tablespaces or dictionary managed tablespaces of the temporary type, or locally managed temporary tablespaces have an extent size of 2 blocks, then LOB segments cannot be created in these tablespaces. This is because in these tablespace types, extent sizes are fixed and the default storage setting of the tablespaces is not ignored.

Choosing a LOB Column Datatype

When selecting a datatype, consider the following topics:

- LOBs Compared to LONG and LONG RAW Types

- Storing Varying-Width Character Data in LOBs

- Implicit Character Set Conversions with LOBs

LOBs Compared to LONG and LONG RAW Types

Table 4-1 lists the similarities and differences between LOBs, LONGs, and LONG RAW types.

Table 4-1 LOBs Vs. LONG RAW

LOB Data Type

LONG and LONG RAW Data Type

You can store multiple LOBs in a single row

You can store only one LONG or LONG RAW in each row.

LOBs can be attributes of a user-defined datatype

This is not possible with either a LONG or LONG RAW

Only the LOB locator is stored in the table column; BLOB and CLOB data can be stored in separate tablespaces and BFILE data is stored as an external file.
For inline LOBs, the database will store LOBs that are less than approximately 4000 bytes of data in the table column.

In the case of a LONG or LONG RAW the entire value is stored in the table column.

When you access a LOB column, you can choose to fetch the locator or the data.

When you access a LONG or LONG RAW, the entire value is returned.

A LOB can be up to 8 terabytes or more in size depending on your block size.

A LONG or LONG RAW instance is limited to 2 gigabytes in size.

There is greater flexibility in manipulating data in a random, piece-wise manner with LOBs. LOBs can be accessed at random offsets.

Less flexibility in manipulating data in a random, piece-wise manner with LONG or LONG RAW data.LONGs must be accessed from the beginning to the desired location.

You can replicate LOBs in both local and distributed environments.

Replication in both local and distributed environments is not possible with a LONG or LONG RAW (see Oracle Database Advanced Replication)

Storing Varying-Width Character Data in LOBs

Varying-width character data in CLOB and NCLOB datatypes is stored in an internal format that is compatible with UCS2 Unicode character set format. This ensures that there is no storage loss of character data in a varying-width format. Also note the following if you are using LOBs to store varying-width character data:

- You can create tables containing CLOB and NCLOB columns even if you use a varying-width CHAR or NCHAR database character set.

- You can create a table containing a datatype that has a CLOB attribute regardless of whether you use a varying-width CHAR database character set.

Implicit Character Set Conversions with LOBs

For CLOB and NCLOB instances used in OCI (Oracle Call Interface), or any of the programmatic environments that access OCI functionality, character set conversions are implicitly performed when translating from one character set to another.

The DBMS_LOB.LOADCLOBFROMFILE API, performs an implicit conversion from binary data to character data when loading to a CLOB or NCLOB. With the exception of DBMS_LOB.LOADCLOBFROMFILE, LOB APIs do not perform implicit conversions from binary data to character data.

For example, when you use the DBMS_LOB.LOADFROMFILE API to populate a CLOB or NCLOB, you are populating the LOB with binary data from a BFILE. In this case, you must perform character set conversions on the BFILE data before calling DBMS_LOB.LOADFROMFILE.

See Also:

Oracle Database Globalization Support Guide for more detail on character set conversions.

Note:

The ALTER DATABASE command will not work when there are CLOB or NCLOB columns in the tables.

Selecting a Table Architecture

When designing your table, consider the following design criteria:

- LOB Storage

- Inline and Out-of-Line LOB Storage

- Defining Tablespace and Storage Characteristics for Persistent LOBs

- LOB Storage Characteristics for LOB Column or Attribute

- TABLESPACE and LOB Index

- PCTVERSION

- CACHE / NOCACHE / CACHE READS

- LOGGING / NOLOGGING

- CHUNK

- ENABLE or DISABLE STORAGE IN ROW Clause

- LOBs in Index Organized Tables

- Manipulating LOBs in Partitioned Tables

- Using Domain Indexing on LOB Columns

LOB Storage

This section summarizes LOB storage characteristics to consider when designing tables with LOB column types.

Inline and Out-of-Line LOB Storage

LOB columns store locators that reference the location of the actual LOB value. Depending on the column properties you specify when you create the table, and depending the size of the LOB, actual LOB values are stored either in the table row (inline) or outside of the table row (out-of-line).

LOB values are stored out-of-line when any of the following situations apply:

- By default. That is, if you do not specify a LOB parameter for the LOB storage clause when you create the table.

- When you explicitly specify DISABLE STORAGE IN ROW for the LOB storage clause when you create the table.

- When the size of the LOB is greater than 3964 bytes, the LOB value for the LOB instance (regardless of the LOB storage properties for the column).

- If you update a LOB that is stored out-of-line and the resulting LOB is less than 3964 bytes in size, it is still stored out-of-line.

LOB values are stored inline when any of the following conditions apply:

- When you explicitly specify ENABLE STORAGE IN ROW for the LOB storage clause when you create the table, and the size of the LOB stored in the given row is small, 4K bytes or less.

- When the LOB value is NULL (regardless of the LOB storage properties for the column).

Using the default LOB storage properties (inline storage) can allow for better database performance; it avoids the overhead of creating and managing out-of-line storage for smaller LOB values. If LOB values stored in your database are frequently small in size, then using inline storage is recommended.

Note:

- LOB locators are always stored in the row.

- A LOB locator always exists for any LOB instance regardless of the LOB storage properties or LOB value - NULL, empty, or otherwise.

- If the table is created with DISABLE STORAGE IN ROW properties and the LOB holds any data, then a minimum of one CHUNK of out-of-line storage space is used; even when the size of the LOB is less than the CHUNK size.

- If a LOB column is initialized with EMPTY_CLOB() or EMPTY_BLOB(), then no LOB value exists, not even NULL. The row holds a LOB locator only. No additional LOB storage is used.

- LOB storage properties do not affect BFILE columns. BFILE data is always stored in operating system files outside the database.

Defining Tablespace and Storage Characteristics for Persistent LOBs

When defining LOBs in a table, you can explicitly indicate the tablespace and storage characteristics for each persistent LOB column as shown in the following example:

CREATE TABLE ContainsLOB_tab (n NUMBER, c CLOB)
lob (c) STORE AS SEGNAME (TABLESPACE lobtbs1 CHUNK 4096
PCTVERSION 5
NOCACHE LOGGING
STORAGE (MAXEXTENTS 5)
);

Note:

There are no tablespace or storage characteristics that you can specify for external LOBs as they are not stored in the database.

If you need to modify the LOB storage parameters on an existing LOB column, then use the MODIFY LOB clause of the ALTER TABLE statement.

Note:

Only some storage parameters can be modified. For example, you can use the ALTER TABLE ... MODIFY LOB statement to change RETENTION, PCTVERSION, CACHE or NO CACHE LOGGING or NO LOGGING, and the STORAGE clause.
You can also change the TABLESPACE using the ALTER TABLE ... MOVE statement.

However, once the table has been created, you cannot change the CHUNK size, or the ENABLE or DISABLE STORAGE IN ROW settings.

Assigning a LOB Data Segment Name

As shown in the in the previous example, specifying a name for the LOB data segment makes for a much more intuitive working environment. When querying the LOB data dictionary views USER_LOBS, ALL_LOBS, DBA_LOBS (see Oracle Database Reference), you see the LOB data segment that you chose instead of system-generated names.

LOB Storage Characteristics for LOB Column or Attribute

LOB storage characteristics that can be specified for a LOB column or a LOB attribute include the following:

- TABLESPACE

- PCTVERSION or RETENTION

Note that you can specify either PCTVERSION or RETENTION, but not both.

- CACHE/NOCACHE/CACHE READS

- LOGGING/NOLOGGING

- CHUNK

- ENABLE/DISABLE STORAGE IN ROW

- STORAGE

For most users, defaults for these storage characteristics will be sufficient. If you want to fine-tune LOB storage, then consider the following guidelines.

See Also:

"STORAGE clause" in Oracle Database SQL Reference

TABLESPACE and LOB Index

Best performance for LOBs can be achieved by specifying storage for LOBs in a tablespace different from the one used for the table that contains the LOB. If many different LOBs will be accessed frequently, then it may also be useful to specify a separate tablespace for each LOB column or attribute in order to reduce device contention.

The LOB index is an internal structure that is strongly associated with LOB storage. This implies that a user may not drop the LOB index and rebuild it.

Note:

The LOB index cannot be altered.

The system determines which tablespace to use for LOB data and LOB index depending on your specification in the LOB storage clause:

- If you do not specify a tablespace for the LOB data, then the tablespace of the table is used for the LOB data and index.

- If you specify a tablespace for the LOB data, then both the LOB data and index use the tablespace that was specified.

Tablespace for LOB Index in Non-Partitioned Table

When creating a table, if you specify a tablespace for the LOB index for a non-partitioned table, then your specification of the tablespace will be ignored and the LOB index will be co-located with the LOB data. Partitioned LOBs do not include the LOB index syntax.

Specifying a separate tablespace for the LOB storage segments will allow for a decrease in contention on the tablespace of the table.

PCTVERSION

When a LOB is modified, a new version of the LOB page is produced in order to support consistent read of prior versions of the LOB value.

PCTVERSION is the percentage of all used LOB data space that can be occupied by old versions of LOB data pages. As soon as old versions of LOB data pages start to occupy more than the PCTVERSION amount of used LOB space, Oracle Database tries to reclaim the old versions and reuse them. In other words, PCTVERSION is the percent of used LOB data blocks that is available for versioning old LOB data.

PCTVERSION has a default of 10 (%), a minimum of 0, and a maximum of 100.

To decide what value PCTVERSION should be set to, consider the following:

- How often LOBs are updated?

- How often the updated LOBs are read?

Table 4-2, "Recommended PCTVERSION Settings" provides some guidelines for determining a suitable PCTVERSION value.

Table 4-2 Recommended PCTVERSION Settings

LOB Update Pattern

LOB Read Pattern

PCTVERSION

Updates XX% of LOB data

Reads updated LOBs

XX%

Updates XX% of LOB data

Reads LOBs but not the updated LOBs

0%

Updates XX% of LOB data

Reads both updated and non-updated LOBs

XX%

Never updates LOB

Reads LOBs

0%

If your application requires several LOB updates concurrent with heavy reads of LOB columns, then consider using a higher value for PCTVERSION, such as 20%.

Setting PCTVERSION to twice the default value allows more free pages to be used for old versions of data pages. Because large queries may require consistent reads of LOB columns, it may be useful to retain old versions of LOB pages. In this case, LOB storage may grow because the database will not reuse free pages aggressively.

If persistent LOB instances in your application are created and written just once and are primarily read-only afterward, then updates are infrequent. In this case, consider using a lower value for PCTVERSION, such as 5% or lower.

The more infrequent and smaller the LOB updates are, the less space must be reserved for old copies of LOB data. If existing LOBs are known to be read-only, then you could safely set PCTVERSION to 0% because there would never be any pages needed for old versions of data.

RETENTION

As an alternative to the PCTVERSION parameter, you can specify the RETENTION parameter in the LOB storage clause of the CREATE TABLE or ALTER TABLE statement. Doing so, configures the LOB column to store old versions of LOB data for a period of time, rather than using a percentage of the table space. For example:

CREATE TABLE ContainsLOB_tab (n NUMBER, c CLOB)
lob (c) STORE AS SEGNAME (TABLESPACE lobtbs1 CHUNK 4096
RETENTION
NOCACHE LOGGING
STORAGE (MAXEXTENTS 5)
);

The RETENTION parameter is designed for use with Undo features of the database, such as Flashback Versions Query. When a LOB column has the RETENTION property set, old versions of the LOB data are retained for the amount of time specified by the UNDO_RETENTION parameter.

Note the following with respect to the RETENTION parameter:

- Undo SQL is not enabled for LOB columns as it is with other datatypes. You must set the RETENTION property on a LOB column to use Undo SQL on LOB data.

- You cannot set the value of the RETENTION parameter explicitly. The amount of time for retention of LOB versions in determined by the UNDO_RETENTION parameter.

- Usage of the RETENTION parameter is only supported in Automatic Undo Management mode. You must configure your table for use with Automatic Undo Management before you can set RETENTION on a LOB column.

- The LOB storage clause can specify RETENTION or PCTVERSION, but not both.

See Also:

- Oracle Database Application Developer's Guide - Fundamentals for more information on using flashback features of the database.

- Oracle Database SQL Reference for details on LOB storage clause syntax.

CACHE / NOCACHE / CACHE READS

When creating tables that contain LOBs, use the cache options according to the guidelines in Table 4-3, "When to Use CACHE, NOCACHE, and CACHE READS":

Table 4-3 When to Use CACHE, NOCACHE, and CACHE READS

Cache Mode

Read

Write

CACHE READS

Frequently

Once or occasionally

CACHE

Frequently

Frequently

NOCACHE (default)

Once or occasionally

Never

CACHE / NOCACHE / CACHE READS: LOB Values and Buffer Cache

- CACHE: Oracle places LOB pages in the buffer cache for faster access.

- NOCACHE: As a parameter in the STORE AS clause, NOCACHE specifies that LOB values are not brought into the buffer cache.

- CACHE READS: LOB values are brought into the buffer cache only during read and not during write operations.

Note:

Using the CACHE option results in improved performance when reading and writing data from the LOB column. However, it can potentially age other non-LOB pages out of the buffer cache prematurely.

LOGGING / NOLOGGING

[NO] LOGGING has a similar application with regard to using LOBs as it does for other table operations. In the usual case, if the [NO]LOGGING clause is omitted, then this means that neither NO LOGGING nor LOGGING is specified and the logging attribute of the table or table partition defaults to the logging attribute of the tablespace in which it resides.

For LOBs, there is a further alternative depending on how CACHE is stipulated.

- CACHE is specified and [NO]LOGGING clause is omitted, LOGGING is automatically implemented (because you cannot have CACHE NOLOGGING).

- CACHE is not specified and [NO]LOGGING clause is omitted, the process defaults in the same way as it does for tables and partitioned tables. That is, the [NO]LOGGING value is obtained from the tablespace in which the LOB value resides.

The following issues should also be kept in mind.

LOBs Will Always Generate Undo for LOB Index Pages

Regardless of whether LOGGING or NOLOGGING is set LOBs will never generate rollback information (undo) for LOB data pages because old LOB data is stored in versions. Rollback information that is created for LOBs tends to be small because it is only for the LOB index page changes.

When LOGGING is Set Oracle Will Generate Full Redo for LOB Data Pages

NOLOGGING is intended to be used when a customer does not care about media recovery. Thus, if the disk/tape/storage media fails, then you will not be able to recover your changes from the log because the changes were never logged.

NOLOGGING is Useful for Bulk Loads or Inserts.

For instance, when loading data into the LOB, if you do not care about redo and can just start the load over if it fails, set the LOB data segment storage characteristics to NOCACHE NOLOGGING. This provides good performance for the initial load of data.

Once you have completed loading data, if necessary, use ALTER TABLE to modify the LOB storage characteristics for the LOB data segment for normal LOB operations, for example, to CACHE or NOCACHE LOGGING.

Note:

CACHE implies that you also get LOGGING.

CHUNK

A chunk is one or more Oracle blocks. You can specify the chunk size for the LOB when creating the table that contains the LOB. This corresponds to the data size used by Oracle Database when accessing or modifying the LOB value. Part of the chunk is used to store system-related information and the rest stores the LOB value. The API you are using has a function that returns the amount of space used in the LOB chunk to store the LOB value. In PL/SQL use DBMS_LOB.GETCHUNKSIZE. In OCI, use OCILobGetChunkSize().

Note:

If the tablespace block size is the same as the database block size, then CHUNK is also a multiple of the database block size. The default CHUNK size is equal to the size of one tablespace block, and the maximum value is 32K.

See Also:

"Terabyte-Size LOB Support" for information about maximum LOB sizes

Choosing the Value of CHUNK

Once the value of CHUNK is chosen (when the LOB column is created), it cannot be changed. Hence, it is important that you choose a value which optimizes your storage and performance requirements.

Space Considerations

The value of CHUNK does not matter for LOBs that are stored inline. This happens when ENABLE STORAGE IN ROW is set, and the size of the LOB locator and the LOB data is less than 4000 bytes. However, when the LOB data is stored out-of-line, it will always take up space in multiples of the CHUNK parameter. This can lead to a large waste of space if your data is small, but the CHUNK is set to a large number. The following table illustrates this point:

Table 4-4 Data Size and CHUNK Size

Data Size

CHUNK Size

Disk Space Used to Store the LOB

Space Utilization (Percent)

3500 enable storage in row

irrelevant

3500 in row

100

3500 disable storage in row

32 KB

32 KB

10

3500 disable storage in row

4 KB

4 KB

90

33 KB

32 KB

64 KB

51

2 GB +10

32 KB

2 GB + 32 KB

99+

Performance Considerations

Accessing lobs in big chunks is more efficient. You can set CHUNK to the data size most frequently accessed or written. For example, if only one block of LOB data is accessed at a time, then set CHUNK to the size of one block. If you have big LOBs, and read or write big amounts of data, then choose a large value for CHUNK.

Set INITIAL and NEXT to Larger than CHUNK

If you explicitly specify storage characteristics for the LOB, then make sure that INITIAL and NEXT for the LOB data segment storage are set to a size that is larger than the CHUNK size. For example, if the database block size is 2KB and you specify a CHUNK of 8KB, then make sure that INITIAL and NEXT are bigger than 8KB and preferably considerably bigger (for example, at least 16KB).

Put another way: If you specify a value for INITIAL, NEXT, or the LOB CHUNK size, then make sure they are set in the following manner:

- CHUNK <= NEXT

- CHUNK <= INITIAL

ENABLE or DISABLE STORAGE IN ROW Clause

You use the ENABLE | DISABLE STORAGE IN ROW clause to indicate whether the LOB should be stored inline (in the row) or out-of-line.

Note:

You may not alter this specification once you have made it: if you ENABLE STORAGE IN ROW, then you cannot alter it to DISABLE STORAGE IN ROW and vice versa.

The default is ENABLE STORAGE IN ROW.

Guidelines for ENABLE or DISABLE STORAGE IN ROW

The maximum amount of LOB data stored in the row is the maximum VARCHAR2 size (4000). This includes the control information as well as the LOB value. If you indicate that the LOB should be stored in the row, once the LOB value and control information is larger than 4000, then the LOB value is automatically moved out of the row.

This suggests the following guidelines:

The default, ENABLE STORAGE IN ROW, is usually the best choice for the following reasons:

- Small LOBs: If the LOB is small (< 4000 bytes), then the whole LOB can be read while reading the row without extra disk I/O.

- Large LOBs: If the LOB is big (> 4000 bytes), then the control information is still stored in the row if ENABLE STORAGE IN ROW is set, even after moving the LOB data out of the row. This control information could enable us to read the out-of-line LOB data faster.

However, in some cases DISABLE STORAGE IN ROW is a better choice. This is because storing the LOB in the row increases the size of the row. This impacts performance if you are doing a lot of base table processing, such as full table scans, multi-row accesses (range scans), or many UPDATE/SELECT to columns other than the LOB columns.

Indexing LOB Columns

This section discusses different techniques you can use to index LOB columns.

Using Domain Indexing on LOB Columns

You might be able to improve the performance of queries by building indexes specifically attuned to your domain. Extensibility interfaces provided with the database allow for domain indexing, a framework for implementing such domain specific indexes.

Note:

You cannot build a B-tree or bitmap index on a LOB column.

See Also:

Oracle Database Data Cartridge Developer's Guide for information on building domain specific indexes.

Indexing LOB Columns Using a Text Index

Depending on the nature of the contents of the LOB column, one of the Oracle Text options could also be used for building indexes. For example, if a text document is stored in a CLOB column, then you can build a text index to speed up the performance of text-based queries over the CLOB column.

See Also:

Oracle Text Reference for more information regarding Oracle Text options.

Function-Based Indexes on LOBs

A function-based index is an index built on an expression. It extends your indexing capabilities beyond indexing on a column. A function-based index increases the variety of ways in which you can access data.

Function-based indexes cannot be built on nested tables or LOB columns. However, you can build function-based indexes on VARRAYs.

Like extensible indexes and domain indexes on LOB columns, function-based indexes are also automatically updated when a DML operation is performed on the LOB column. Function-based indexes are also updated when any extensible index is updated.

See Also:

Oracle Database Application Developer's Guide - Fundamentals for more information on using function-based indexes

Extensible Indexing on LOB Columns

The database provides extensible indexing, a feature which enables you to define new index types as required. This is based on the concept of cooperative indexing where a data cartridge and the database build and maintain indexes for data types such as text and spatial for example, for On-line-Analytical Processing (OLAP).

The cartridge is responsible for defining the index structure, maintaining the index content during load and update operations, and searching the index during query processing. The index structure can be stored in Oracle as heap-organized, or an index-organized table, or externally as an operating system file.

To support this structure, the database provides an indextype. The purpose of an indextype is to enable efficient search and retrieval functions for complex domains such as text, spatial, image, and OLAP by means of a data cartridge. An indextype is analogous to the sorted or bit-mapped index types that are built-in within the Oracle Server. The difference is that an indextype is implemented by the data cartridge developer, whereas the Oracle kernel implements built-in indexes. Once a new indextype has been implemented by a data cartridge developer, end users of the data cartridge can use it just as they would built-in indextypes.

When the database system handles the physical storage of domain indexes, data cartridges

- Define the format and content of an index. This enables cartridges to define an index structure that can accommodate a complex data object.

- Build, delete, and update a domain index. The cartridge handles building and maintaining the index structures. Note that this is a significant departure from the medicine indexing features provided for simple SQL data types. Also, because an index is modeled as a collection of tuples, in-place updating is directly supported.

- Access and interpret the content of an index. This capability enables the data cartridge to become an integral component of query processing. That is, the content-related clauses for database queries are handled by the data cartridge.

By supporting extensible indexes, the database significantly reduces the effort needed to develop high-performance solutions that access complex datatypes such as LOBs.

Extensible Optimizer

The extensible optimizer functionality allows authors of user-defined functions and indexes to create statistics collections, selectivity, and cost functions. This information is used by the optimizer in choosing a query plan. The cost-based optimizer is thus extended to use the user-supplied information.

Extensible indexing functionality enables you to define new operators, index types, and domain indexes. For such user-defined operators and domain indexes, the extensible optimizer functionality will allow users to control the three main components used by the optimizer to select an execution plan: statistics, selectivity, and cost.

See Also:

Oracle Database Data Cartridge Developer's Guide

Oracle Text Indexing Support for XML

You can create Oracle Text indexes on CLOB columns and perform queries on XML data.

See Also:

- Oracle XML Developer's Kit Programmer's Guide

- Oracle Text Reference

- Oracle Text Application Developer's Guide

Manipulating LOBs in Partitioned Tables

You can partition tables that contain LOB columns. As a result, LOBs can take advantage of all of the benefits of partitioning including the following:

- LOB segments can be spread between several tablespaces to balance I/O load and to make backup and recovery more manageable.

- LOBs in a partitioned table become easier to maintain.

- LOBs can be partitioned into logical groups to speed up operations on LOBs that are accessed as a group.

This section describes some of the ways you can manipulate LOBs in partitioned tables.

Partitioning a Table Containing LOB Columns

LOBs are supported in RANGE partitioned, LIST partitioned, and HASH partitioned tables. Composite heap-organized tables can also have LOBs.

You can partition a table containing LOB columns using the following techniques:

- When the table is created using the PARTITION BY ... clause of the CREATE TABLE statement.

- Adding a partition to an existing table using the ALTER TABLE ... ADD PARTITION clause.

- Exchanging partitions with a table that already has partitioned LOB columns using the ALTER TABLE ... EXCHANGE PARTITION clause. Note that EXCHANGE PARTITION can only be used when both tables have the same storage attributes, for example, both tables store LOBs out-of-line.

Creating LOB partitions at the same time you create the table (in the CREATE TABLE statement) is recommended. If you create partitions on a LOB column when the table is created, then the column can hold LOBs stored either inline or out-of-line LOBs.

After a table is created, new LOB partitions can only be created on LOB columns that are stored out-of-line. Also, partition maintenance operations, SPLIT PARTITION and MERGE PARTITIONS, will only work on LOB columns that store LOBs out-of-line.

See Also:

"Restrictions for LOBs in Partitioned Index-Organized Tables" for additional information on LOB restrictions.

Note that once a table is created, storage attributes cannot be changed. See "LOB Storage" for more information about LOB storage attributes.

Creating an Index on a Table Containing Partitioned LOB Columns

To improve the performance of queries, you can create indexes on partitioned LOB columns. For example:

CREATE INDEX index_name
ON table_name (LOB_column_1, LOB_column_2, ...) LOCAL;

Note that only domain and function-based indexes are supported on LOB columns. Other types of indexes, such as unique indexes are not supported with LOBs.

Moving Partitions Containing LOBs

You can move a LOB partition into a different tablespace. This is useful if the tablespace is no longer large enough to hold the partition. To do so, use the ALTER TABLE ... MOVE PARTITION clause. For example:

ALTER TABLE current_table MOVE PARTITION partition_name
TABLESPACE destination_table_space
LOB (column_name) STORE AS (TABLESPACE current_tablespace);

Splitting Partitions Containing LOBs

You can split a partition containing LOBs into two equally sized partitions using the ALTER TABLE ... SPLIT PARTITION clause. Doing so permits you to place one or both new partitions in a new tablespace. For example:

ALTER TABLE table_name SPLIT PARTITION partition_name
AT (partition_range_upper_bound)
INTO (PARTITION partition_name,
PARTITION new_partition_name TABLESPACE new_tablespace_name
LOB (column_name) STORE AS (TABLESPACE tablespace_name)
... ;

Merging Partitions Containing LOBs

You can merge partitions that contain LOB columns using the ALTER TABLE ... MERGE PARTITIONS clause. This technique is useful for reclaiming unused partition space. For example:

ALTER TABLE table_name
MERGE PARTITIONS partition_1, partition_2
INTO PARTITION new_partition TABLESPACE new_tablespace_name
LOB (column_name) store as (TABLESPACE tablespace_name)
... ;

LOBs in Index Organized Tables

Index Organized Tables (IOTs) support internal and external LOB columns. For the most part, SQL DDL, DML, and piece wise operations on LOBs in IOTs produce the same results as those for normal tables. The only exception is the default semantics of LOBs during creation. The main differences are:

- Tablespace Mapping: By default, or unless specified otherwise, the LOB data and index segments will be created in the tablespace in which the primary key index segments of the index organized table are created.

- Inline as Compared to Out-of-Line Storage: By default, all LOBs in an index organized table created without an overflow segment will be stored out of line. In other words, if an index organized table is created without an overflow segment, then the LOBs in this table have their default storage attributes as DISABLE STORAGE IN ROW. If you forcibly try to specify an ENABLE STORAGE IN ROW clause for such LOBs, then SQL will raise an error.

On the other hand, if an overflow segment has been specified, then LOBs in index organized tables will exactly mimic their semantics in conventional tables (see "Defining Tablespace and Storage Characteristics for Persistent LOBs").

Example of Index Organized Table (IOT) with LOB Columns

Consider the following example:

CREATE TABLE iotlob_tab (c1 INTEGER PRIMARY KEY, c2 BLOB, c3 CLOB, c4
VARCHAR2(20))
ORGANIZATION INDEX
TABLESPACE iot_ts
PCTFREE 10 PCTUSED 10 INITRANS 1 MAXTRANS 1 STORAGE (INITIAL 4K)
PCTTHRESHOLD 50 INCLUDING c2
OVERFLOW
TABLESPACE ioto_ts
PCTFREE 10 PCTUSED 10 INITRANS 1 MAXTRANS 1 STORAGE (INITIAL 8K) LOB (c2)
STORE AS lobseg (TABLESPACE lob_ts DISABLE STORAGE IN ROW
CHUNK 16384 PCTVERSION 10 CACHE STORAGE (INITIAL 2M)
INDEX lobidx_c1 (TABLESPACE lobidx_ts STORAGE (INITIAL 4K)));

Executing these statements will result in the creation of an index organized table iotlob_tab with the following elements:

- A primary key index segment in the tablespace iot_ts,

- An overflow data segment in tablespace ioto_ts

- Columns starting from column C3 being explicitly stored in the overflow data segment

- BLOB (column C2) data segments in the tablespace lob_ts

- BLOB (column C2) index segments in the tablespace lobidx_ts

- CLOB (column C3) data segments in the tablespace iot_ts

- CLOB (column C3) index segments in the tablespace iot_ts

- CLOB (column C3) stored in line by virtue of the IOT having an overflow segment

- BLOB (column C2) explicitly forced to be stored out of line

Note:

If no overflow had been specified, then both C2 and C3 would have been stored out of line by default.

Other LOB features, such as BFILEs and varying character width LOBs, are also supported in index organized tables, and their usage is the same as for conventional tables.

Restrictions for LOBs in Partitioned Index-Organized Tables

LOB columns are supported in range-, list-, and hash-partitioned index-organized tables with the following restrictions:

- Composite partitioned index-organized tables are not supported.

- Relational and object partitioned index-organized tables (partitioned by range, hash, or list) can hold LOBs stored as follows; however, partition maintenance operations, such as MOVE, SPLIT, and MERGE are not supported with:

- VARRAY datatypes stored as LOB datatypes

- Abstract datatypes with LOB attributes

- Nested tables with LOB types

See Also:

Additional restrictions for LOB columns in general are given in "LOB Rules and Restrictions".

Updating LOBs in Nested Tables

To update LOBs in a nested table, you must lock the row containing the LOB explicitly. To do so, you must specify the FOR UPDATE clause in the subquery prior to updating the LOB value.

Note that locking the row of a parent table does not lock the row of a nested table containing LOB columns.

Note:

Nested tables containing LOB columns are the only data structures supported for creating collections of LOBs. You cannot create a VARRAY of any LOB datatype.

5 Advanced Design Considerations

This chapter describes design considerations for more advanced application development issues.

This chapter contains these topics:

- LOB Buffering Subsystem

- Opening Persistent LOBs with the OPEN and CLOSE Interfaces

- Read Consistent Locators

- LOB Locators and Transaction Boundaries

- LOBs in the Object Cache

- Terabyte-Size LOB Support

- Guidelines for Creating Gigabyte LOBs

LOB Buffering Subsystem

The database provides a LOB buffering subsystem (LBS) for advanced OCI-based applications such as Data Cartridges, Web servers, and other client-based applications that need to buffer the contents of one or more LOBs in the client address space. The client-side memory requirement for the buffering subsystem during its maximum usage is 512 KBytes. It is also the maximum amount that you can specify for a single read or write operation on a LOB that has been enabled for buffered access.

Advantages of LOB Buffering

The advantages of buffering, especially for client applications that perform a series of small reads and writes (often repeatedly) to specific regions of the LOB, are:

- Buffering enables deferred writes to the server. You can buffer up several writes in the LOB buffer in the client address space and eventually flush the buffer to the server. This reduces the number of network round-trips from your client application to the server, and hence, makes for better overall performance for LOB updates.

- Buffering reduces the overall number of LOB updates on the server, thereby reducing the number of LOB versions and amount of logging. This results in better overall LOB performance and disk space usage.

Guidelines for Using LOB Buffering

The following caveats apply to buffered LOB operations:

- Explicitly flush LOB buffer contents. The LOB buffering subsystem is not a cache. The contents of a LOB buffer are not always the same as the LOB value in the server. Unless you explicitly flush the contents of a LOB buffer, you will not see the results of your buffered writes reflected in the actual LOB on the server.

- Error recovery for buffered LOB operations is your responsibility. Owing to the deferred nature of the actual LOB update, error reporting for a particular buffered read or write operation is deferred until the next access to the server based LOB.

- LOB Buffering is Single User, Single Threaded. Transactions involving buffered LOB operations cannot migrate across user sessions — the LBS is a single user, single threaded system.

- Maintain logical savepoints to rollback to. Oracle does not guarantee transactional support for buffered LOB operations. To ensure transactional semantics for buffered LOB updates, you must maintain logical savepoints in your application to rollback all the changes made to the buffered LOB in the event of an error. You should always wrap your buffered LOB updates within a logical savepoint (see "OCI Example of LOB Buffering").

- Ensure LOB is not updated by another bypassing transaction. In any given transaction, once you have begun updating a LOB using buffered writes, it is your responsibility to ensure that the same LOB is not updated through any other operation within the scope of the same transaction that bypasses the buffering subsystem.

You could potentially do this by using an SQL statement to update the server-based LOB. Oracle cannot distinguish, and hence prevent, such an operation. This will seriously affect the correctness and integrity of your application.

- Updating buffer-enabled LOB locators. Buffered operations on a LOB are done through its locator, just as in the conventional case. A locator that is enabled for buffering will provide a consistent read version of the LOB, until you perform a write operation on the LOB through that locator. See also, "Read Consistent Locators".

Once the locator becomes an updated locator by virtue of its being used for a buffered write, it will always provide access to the most up-to-date version of the LOB as seen through the buffering subsystem. Buffering also imposes an additional significance to this updated locator — all further buffered writes to the LOB can be done only through this updated locator. Oracle will return an error if you attempt to write to the LOB through other locators enabled for buffering. See also, "Example of Updating LOBs Through Updated Locators".

- Passing a buffer-enabled LOB locator an IN OUT or OUT parameter. You can pass an updated locator that was enabled for buffering as an IN parameter to a PL/SQL procedure. However, passing an IN OUT or an OUT parameter will produce an error, as will an attempt to return an updated locator.

- You cannot assign an updated locator that was enabled for buffering to another locator. There are a number of different ways that assignment of locators may occur — through OCILobAssign(), through assignment of PL/SQL variables, through OCIObjectCopy() where the object contains the LOB attribute, and so on. Assigning a consistent read locator that was enabled for buffering to a locator that did not have buffering enabled, turns buffering on for the target locator. By the same token, assigning a locator that was not enabled for buffering to a locator that did have buffering enabled, turns buffering off for the target locator.

Similarly, if you SELECT into a locator for which buffering was originally enabled, then the locator becomes overwritten with the new locator value, thereby turning buffering off.

- When two or more locators point to the same LOB do not enable both for buffering. If two or more different locators point to the same LOB, then it is your responsibility to make sure that you do not enable both the locators for buffering. Otherwise Oracle does not guarantee the contents of the LOB.

- Buffer-enable LOBs do not support appends that create zero-byte fillers or spaces. Appending to the LOB value using buffered write(s) is allowed, but only if the starting offset of these write(s) is exactly one byte (or character) past the end of the BLOB (or CLOB/NCLOB). In other words, the buffering subsystem does not support appends that involve creation of zero-byte fillers or spaces in the server based LOB.

- For CLOBs, Oracle requires the client side character set form for the locator bind variable be the same as that of the LOB in the server. This is usually the case in most OCI LOB programs. The exception is when the locator is selected from a remote database, which may have a different character set form from the database which is currently being accessed by the OCI program. In such a case, an error is returned. If there is no character set form input by the user, then Oracle assumes it is SQLCS_IMPLICIT.

LOB Buffering Subsystem Usage

Here are some details of the LOB buffering subsystem:

LOB Buffer Physical Structure

Each user session has the following structure:

- Fixed page pool of 16 pages, shared by all LOBs accessed in buffering mode from that session.

- Each page has a fixed size of up to 32K bytes (not characters) where page size = n x CHUNK ~= 32K.

A LOB buffer consists of one or more of these pages, up to a maximum of 16 in each session. The maximum amount that you ought to specify for any given buffered read or write operation is 512K bytes, remembering that under different circumstances the maximum amount you may read/write could be smaller.

LOB Buffering Subsystem Usage Scenario

Consider that a LOB is divided into fixed-size, logical regions. Each page is mapped to one of these fixed size regions, and is in essence, their in-memory copy. Depending on the input offset and amount specified for a read or write operation, the database allocates one or more of the free pages in the page pool to the LOB buffer. A free page is one that has not been read or written by a buffered read or write operation.

For example, assuming a page size of 32KBytes:

- For an input offset of 1000 and a specified read/write amount of 30000, Oracle reads the first 32K byte region of the LOB into a page in the LOB buffer.

- For an input offset of 33000 and a read/write amount of 30000, the second 32K region of the LOB is read into a page.

- For an input offset of 1000, and a read/write amount of 35000, the LOB buffer will contain two pages — the first mapped to the region 1 — 32K, and the second to the region 32K+1 — 64K of the LOB.

This mapping between a page and the LOB region is temporary until Oracle maps another region to the page. When you attempt to access a region of the LOB that is not already available in full in the LOB buffer, Oracle allocates any available free page(s) from the page pool to the LOB buffer. If there are no free pages available in the page pool, then Oracle reallocates the pages as follows. It ages out the least recently used page among the unmodified pages in the LOB buffer and reallocates it for the current operation.

If no such page is available in the LOB buffer, then it ages out the least recently used page among the unmodified pages of other buffered LOBs in the same session. Again, if no such page is available, then it implies that all the pages in the page pool are modified, and either the currently accessed LOB, or one of the other LOBs, need to be flushed. Oracle notifies this condition to the user as an error. Oracle never flushes and reallocates a modified page implicitly. You can either flush them explicitly, or discard them by disabling buffering on the LOB.

To illustrate the preceding discussion, consider two LOBs being accessed in buffered mode — L1 and L2, each with buffers of size 8 pages. Assume that 6 of the 8 pages in the L1 buffer are dirty, with the remaining 2 containing unmodified data read in from the server. Assume similar conditions in the L2 buffer. Now, for the next buffered operation on L1, Oracle will reallocate the least recently used page from the two unmodified pages in the L1 buffer. Once all the 8 pages in the L1 buffer are used up for LOB writes, Oracle can service two more operations on L1 by allocating the two unmodified pages from the L2 buffer using the least recently used policy. But for any further buffered operations on L1 or L2, Oracle returns an error.

If all the buffers are dirty and you attempt another read from or write to a buffered LOB, then you will receive the following error:

Error 22280: no more buffers available for operation

There are two possible causes:

1. All buffers in the buffer pool have been used up by previous operations.
In this case, flush the LOBs through the locator that is being used to update the LOB.

2. You are trying to flush a LOB without any previous buffered update operations.
In this case, write to the LOB through a locator enabled for buffering before attempting to flush buffers.

Flushing the LOB Buffer

The term flush refers to a set of processes. Writing data to the LOB in the buffer through the locator transforms the locator into an updated locator. Once you have updated the LOB data in the buffer through the updated locator, a flush call will

- Write the dirty pages in the LOB buffer to the server-based LOB, thereby updating the LOB value,

- Reset the updated locator to be a read consistent locator, and

- Free the flushed buffers or turn the status of the buffer pages back from dirty to unmodified.

After the flush, the locator becomes a read consistent locator and can be assigned to another locator (L2 := L1).

For instance, suppose you have two locators, L1 and L2. Let us say that they are both read consistent locators and consistent with the state of the LOB data in the server. If you then update the LOB by writing to the buffer, L1 becomes an updated locator. L1 and L2 now refer to different versions of the LOB value. If you want to update the LOB in the server, then you must use L1 to retain the read consistent state captured in L2. The flush operation writes a new snapshot environment into the locator used for the flush. The important point to remember is that you must use the updated locator (L1), when you flush the LOB buffer. Trying to flush a read consistent locator will generate an error.

The technique you use to flush the LOB buffer determines whether data in the buffer is cleared and has performance implications as follows:

- In the default mode, data is retained in the pages that were modified when the flush operation occurs. In this case, when you read or write to the same range of bytes, no round-trip to the server is necessary. Note that flushing the buffer, in this context, does not clear the data in the buffer. It also does not return the memory occupied by the flushed buffer to the client address space.

Note:

Unmodified pages may now be aged out if necessary.

- In the second case, you set the flag parameter in OCILobFlushBuffer() to OCI_LOB_BUFFER_FREE to free the buffer pages, and so return the memory to the client address space. Flushing the buffer using this technique updates the LOB value on the server, returns a read consistent locator, and frees the buffer pages.

Flushing the Updated LOB

It is very important to note that you must flush a LOB that has been updated through the LOB buffering subsystem in the following situations:

- Before committing the transaction

- Before migrating from the current transaction to another

- Before disabling buffering operations on a LOB

- Before returning from an external callout execution into the calling function, procedure, or method in PL/SQL

Note that when the external callout is called from a PL/SQL block and the locator is passed as a parameter, all buffering operations, including the enable call, should be made within the callout itself. In other words, adhere to the following sequence:

- Call the external callout

- Enable the locator for buffering

- Read or write using the locator

- Flush the LOB

- Disable the locator for buffering

- Return to the calling function, procedure, or method in PL/SQL

Remember that the database never implicitly flushes the LOB buffer.

Using Buffer-Enabled Locators

Note that there are several cases in which you can use buffer-enabled locators and others in which you cannot.

- When it is OK to Use Buffer-Enabled Locators:

- OCI — A locator that is enabled for buffering can only be used with the following OCI APIs:

OCILobRead2(), OCILobWrite2(), OCILobAssign(), OCILobIsEqual(), OCILobLocatorIsInit(), OCILobCharSetId(), OCILobCharSetForm()

- When it is Not OK to Use Buffer-Enabled Locators: The following OCI APIs will return errors if used with a locator enabled for buffering:

- OCI — OCILobCopy2(), OCILobAppend(), OCILobErase2(), OCILobGetLength2(), OCILobTrim2(), OCILobWriteAppend2()

These APIs will also return errors when used with a locator which has not been enabled for buffering, but the LOB that the locator represents is already being accessed in buffered mode through some other locator.

- PL/SQL (DBMS_LOB) — An error is returned from DBMS_LOB APIs if the input lob locator has buffering enabled.

- As in the case of all other locators, buffer-enabled locators cannot span transactions.

Saving Locator State to Avoid a Reselect

Suppose you want to save the current state of the LOB before further writing to the LOB buffer. In performing updates while using LOB buffering, writing to an existing buffer does not make a round-trip to the server, and so does not refresh the snapshot environment in the locator. This would not be the case if you were updating the LOB directly without using LOB buffering. In that case, every update would involve a round-trip to the server, and so would refresh the snapshot in the locator.

Therefore to save the state of a LOB that has been written through the LOB buffer, follow these steps:

1. Flush the LOB, thereby updating the LOB and the snapshot environment in the locator (L1). At this point, the state of the locator (L1) and the LOB are the same.

2. Assign the locator (L1) used for flushing and updating to another locator (L2). At this point, the states of the two locators (L1 and L2), as well as the LOB are all identical.

L2 now becomes a read consistent locator with which you are able to access the changes made through L1 up until the time of the flush, but not after. This assignment avoids incurring a round-trip to the server to reselect the locator into L2.

OCI Example of LOB Buffering

The following OCI pseudocode example is based on the PM schema included with the Oracle Database Sample Schemas.

OCI_BLOB_buffering_program()
{
int            amount;
int            offset;
OCILobLocator  lbs_loc1, lbs_loc2, lbs_loc3;
void          *buffer;
int            bufl;

-- Standard OCI initialization operations - logging on to
-- server, creating and initializing bind variables...

init_OCI();

-- Establish a savepoint before start of LOB buffering subsystem
-- operations
exec_statement("savepoint lbs_savepoint");

-- Initialize bind variable to BLOB columns from buffered
-- access:
exec_statement("select ad_composite into lbs_loc1 from Print_media
where ad_id = 12001");
exec_statement("select ad_composite into lbs_loc2 from Print_media
where ad_id = 12001 for update");
exec_statement("select ad_composite into lbs_loc2 from Print_media
where ad_id = 12001 for update");

-- Enable locators for buffered mode access to LOB:
OCILobEnableBuffering(..., lbs_loc1);
OCILobEnableBuffering(..., lbs_loc2);
OCILobEnableBuffering(..., lbs_loc3);

-- Read 4K bytes through lbs_loc1 starting from offset 1:
amount = 4096; offset = 1; bufl = 4096;
OCILobRead2(.., lbs_loc1, &amount, 0, offset, buffer, bufl, ...);
if (exception)
goto exception_handler;
-- This will read the first 32K bytes of the LOB from
-- the server into a page (call it page_A) in the LOB
-- client-side buffer.
-- lbs_loc1 is a read consistent locator.

-- Write 4K of the LOB throgh lbs_loc2 starting from
-- offset 1:
amount = 4096; offset = 1; bufl = 4096;
buffer = populate_buffer(4096);
OCILobWrite2(.., lbs_loc2, &amount, 0, offset, buffer, bufl, ..);

if (exception)
goto exception_handler;
-- This will read the first 32K bytes of the LOB from
-- the server into a new page (call it page_B) in the
-- LOB buffer, and modify the contents of this page
-- with input buffer contents.
-- lbs_loc2 is an updated locator.

-- Read 20K bytes through lbs_loc1 starting from
-- offset 10K
amount = 20480; offset = 10240;
OCILobRead2(.., lbs_loc1, &amount, 0, offset, buffer, bufl, ..);

if (exception)
goto exception_handler;
-- Read directly from page_A into the user buffer.
-- There is no round-trip to the server because the
-- data is already in the client-side buffer.

-- Write 20K bytes through lbs_loc2 starting from offset
-- 10K
amount = 20480; offset = 10240; bufl = 20480;
buffer = populate_buffer(20480);
OCILobWrite2(.., lbs_loc2, &amount, 0, offset, buffer, bufl, ..);

if (exception)
goto exception_handler;
-- The contents of the user buffer will now be written
-- into page_B without involving a round-trip to the
-- server.  This avoids making a new LOB version on the
-- server and writing redo to the log.

-- The following write through lbs_loc3 will also
-- result in an error:
amount = 20000; offset = 1000; bufl = 20000;
buffer = populate_buffer(20000);
OCILobWrite2(.., lbs_loc3, amount, 0, offset,buffer, bufl, ..);

if (exception)
goto exception_handler;
-- No two locators can be used to update a buffered LOB
-- through the buffering subsystem

-- The following update through lbs_loc3 will also
-- result in an error
OCILobFileCopy(.., lbs_loc3, lbs_loc2, ..);

if (exception)
goto exception_handler;
-- Locators enabled for buffering cannot be used with
-- operations like Append, Copy, Trim and so on
-- When done, flush the LOB buffer to the server:
OCILobFlushBuffer(.., lbs_loc2, OCI_LOB_BUFFER_NOFREE);

if (exception)
goto exception_handler;
-- This flushes all the modified pages in the LOB buffer,
-- and resets lbs_loc2 from updated to read consistent
-- locator. The modified pages remain in the buffer
-- without freeing memory.  These pages can be aged
-- out if necessary.

-- Disable locators for buffered mode access to LOB */
OCILobDisableBuffering(..., lbs_loc1);
OCILobDisableBuffering(..., lbs_loc2);
OCILobDisableBuffering(..., lbs_loc3);

if (exception)
goto exception_handler;
-- This disables the three locators for buffered access,
-- and frees up the LOB buffer resources.
exception_handler:
handle_exception_reporting();
exec_statement("rollback to savepoint lbs_savepoint");
}

Opening Persistent LOBs with the OPEN and CLOSE Interfaces

The OPEN and CLOSE interfaces enable you to explicitly open a persistent LOB instance. When you open a LOB instance with the OPEN interface, the instance remains open until you explicitly close the LOB using the CLOSE interface. The ISOPEN interface enables you to determine whether a persistent LOB is already open.

Note that the open state of a LOB is associated with the LOB instance, not the LOB locator. The locator does not save any information indicating whether the LOB instance that it points to is open.

See Also:

"Opening and Closing LOBs" for general information on situations that you would open a LOB instance.

Index Performance Benefits of Explicitly Opening a LOB

Explicitly opening a LOB instance can benefit performance of a persistent LOB in an indexed column.

If you do not explicitly open the LOB instance, then every modification to the LOB implicitly opens and closes the LOB instance. Any triggers on a domain index are fired each time the LOB is closed. Note that in this case, any domain indexes on the LOB are updated as soon as any modification to the LOB instance is made; the domain index is always valid and can be used at any time.

When you explicitly open a LOB instance, index triggers do not fire until you explicitly close the LOB. Using this technique can increase performance on index columns by eliminating unneeded indexing events until you explicitly close the LOB. Note that any index on the LOB column is not valid until you explicitly close the LOB.

Working with Explicitly Open LOB Instances

If you explicitly open a LOB instance, then you must close the LOB before you commit the transaction.

Committing a transaction on the open LOB instance will cause an error. When this error occurs, the LOB instance is closed implicitly, any modifications to the LOB instance are saved, and the transaction is committed, but any indexes on the LOB column are not updated. In this situation, you must rebuild your indexes on the LOB column.

If you subsequently rollback the transaction, then the LOB instance is rolled back to its previous state, but the LOB instance is no longer explicitly open.

You must close any LOB instance that you explicitly open:

- Between DML statements that start a transaction, including SELECT ... FOR UPDATE and COMMIT

- Within an autonomous transaction block

- Before the end of a session (when there is no transaction involved)

If you do not explicitly close the LOB instance, then it is implicitly closed at the end of the session and no index triggers are fired.

Keep track of the open or closed state of LOBs that you explicitly open. The following will cause an error:

- Explicitly opening a LOB instance that is already explicitly open.

- Explicitly closing a LOB instance that is already explicitly closed.

This occurs whether you access the LOB instance using the same locator or different locators.

Read Consistent Locators

Oracle Database provides the same read consistency mechanisms for LOBs as for all other database reads and updates of scalar quantities. Refer to Oracle Database Concepts for general information about read consistency. Read consistency has some special applications to LOB locators that you must understand. These applications are described in the following sections.

A Selected Locator Becomes a Read Consistent Locator

A selected locator, regardless of the existence of the FOR UPDATE clause, becomes a read consistent locator, and remains a read consistent locator until the LOB value is updated through that locator. A read consistent locator contains the snapshot environment as of the point in time of the SELECT operation.

This has some complex implications. Suppose you have created a read consistent locator (L1) by way of a SELECT operation. In reading the value of the persistent LOB through L1, note the following:

- The LOB is read as of the point in time of the SELECT statement even if the SELECT statement includes a FOR UPDATE.

- If the LOB value is updated through a different locator (L2) in the same transaction, then L1 does not see the L2 updates.

- L1 will not see committed updates made to the LOB through another transaction.

- If the read consistent locator L1 is copied to another locator L2 (for example, by a PL/SQL assignment of two locator variables — L2:= L1), then L2 becomes a read consistent locator along with L1 and any data read is read as of the point in time of the SELECT for L1.

You can use the existence of multiple locators to access different transformations of the LOB value. However, in doing so, you must keep track of the different values accessed by different locators.

Example of Updating LOBs and Read-Consistency

Read consistent locators provide the same LOB value regardless of when the SELECT occurs.

The following example demonstrates the relationship between read-consistency and updating in a simple example. Using the Print_media table and PL/SQL, three CLOB instances are created as potential locators:

- clob_selected

- clob_update

- clob_copied

Observe these progressions in the code, from times t1 through t6:

- At the time of the first SELECT INTO (at t1), the value in ad_sourcetext is associated with the locator clob_selected.

- In the second operation (at t2), the value in ad_sourcetext is associated with the locator clob_updated. Because there has been no change in the value of ad_sourcetext between t1 and t2, both clob_selected and clob_updated are read consistent locators that effectively have the same value even though they reflect snapshots taken at different moments in time.

- The third operation (at t3) copies the value in clob_selected to clob_copied. At this juncture, all three locators see the same value. The example demonstrates this with a series of DBMS_LOB.READ() calls.

- At time t4, the program uses DBMS_LOB.WRITE() to alter the value in clob_updated, and a DBMS_LOB.READ() reveals a new value.

- However, a DBMS_LOB.READ() of the value through clob_selected (at t5) reveals that it is a read consistent locator, continuing to refer to the same value as of the time of its SELECT.

- Likewise, a DBMS_LOB.READ() of the value through clob_copied (at t6) reveals that it is a read consistent locator, continuing to refer to the same value as clob_selected.

INSERT INTO PRINT_MEDIA VALUES (2056, 20020, EMPTY_BLOB(),
'abcd', EMPTY_CLOB(), EMPTY_CLOB(), NULL, NULL, NULL, NULL);

COMMIT;

DECLARE
num_var           INTEGER;
clob_selected     CLOB;
clob_updated      CLOB;
clob_copied       CLOB;
read_amount       INTEGER;
read_offset       INTEGER;
write_amount      INTEGER;
write_offset      INTEGER;
buffer            VARCHAR2(20);

BEGIN
-- At time t1:
SELECT ad_sourcetext INTO clob_selected
FROM Print_media
WHERE ad_id = 20020;

-- At time t2:
SELECT ad_sourcetext INTO clob_updated
FROM Print_media
WHERE ad_id = 20020
FOR UPDATE;

-- At time t3:
clob_copied := clob_selected;
-- After the assignment, both the clob_copied and the
-- clob_selected have the same snapshot as of the point in time
-- of the SELECT into clob_selected

-- Reading from the clob_selected and the clob_copied will
-- return the same LOB value. clob_updated also sees the same
-- LOB value as of its select:
read_amount := 10;
read_offset := 1;
dbms_lob.read(clob_selected, read_amount, read_offset, buffer);
dbms_output.put_line('clob_selected value: ' || buffer);
-- Produces the output 'abcd'

read_amount := 10;
dbms_lob.read(clob_copied, read_amount, read_offset, buffer);
dbms_output.put_line('clob_copied value: ' || buffer);
-- Produces the output 'abcd'

read_amount := 10;
dbms_lob.read(clob_updated, read_amount, read_offset, buffer);
dbms_output.put_line('clob_updated value: ' || buffer);
-- Produces the output 'abcd'

-- At time t4:
write_amount := 3;
write_offset := 5;
buffer := 'efg';
dbms_lob.write(clob_updated, write_amount, write_offset, buffer);

read_amount := 10;
dbms_lob.read(clob_updated, read_amount, read_offset, buffer);
dbms_output.put_line('clob_updated value: ' || buffer);
-- Produces the output 'abcdefg'

-- At time t5:
read_amount := 10;
dbms_lob.read(clob_selected, read_amount, read_offset, buffer);
dbms_output.put_line('clob_selected value: ' || buffer);
-- Produces the output 'abcd'

-- At time t6:
read_amount := 10;
dbms_lob.read(clob_copied, read_amount, read_offset, buffer);
dbms_output.put_line('clob_copied value: ' || buffer);
-- Produces the output 'abcd'
END;
/

Example of Updating LOBs Through Updated Locators

When you update the value of the persistent LOB through the LOB locator (L1), L1 (that is, the locator itself) is updated to contain the current snapshot environment as of the point in time after the operation was completed on the LOB value through locator L1. L1 is then termed an updated locator. This operation enables you to see your own changes to the LOB value on the next read through the same locator, L1.

Note:

The snapshot environment in the locator is not updated if the locator is used to merely read the LOB value. It is only updated when you modify the LOB value through the locator using the PL/SQL DBMS_LOB package or the OCI LOB APIs.

Any committed updates made by a different transaction are seen by L1 only if your transaction is a read-committed transaction and if you use L1 to update the LOB value after the other transaction committed.

Note:

When you update a persistent LOB value, the modification is always made to the most current LOB value.

Updating the value of the persistent LOB through any of the available methods, such as OCI LOB APIs or PL/SQL DBMS_LOB package, updates the LOB value and then reselects the locator that refers to the new LOB value.

Note that updating the LOB value through SQL is merely an UPDATE statement. It is up to you to do the reselect of the LOB locator or use the RETURNING clause in the UPDATE statement so that the locator can see the changes made by the UPDATE statement. Unless you reselect the LOB locator or use the RETURNING clause, you may think you are reading the latest value when this is not the case. For this reason you should avoid mixing SQL DML with OCI and DBMS_LOB piecewise operations.

See Also:

Oracle Database PL/SQL User's Guide and Reference

Example of Updating a LOB Using SQL DML and DBMS_LOB

Using table Print_media in the following example, a CLOB locator is created as clob_selected. Note the following progressions in the example, from times t1 through t3:

- At the time of the first SELECT INTO (at t1), the value in ad_sourcetext is associated with the locator clob_selected.

- In the second operation (at t2), the value in ad_sourcetext is modified through the SQL UPDATE statement, without affecting the clob_selected locator. The locator still sees the value of the LOB as of the point in time of the original SELECT. In other words, the locator does not see the update made using the SQL UPDATE statement. This is illustrated by the subsequent DBMS_LOB.READ call.

- The third operation (at t3) re-selects the LOB value into the locator clob_selected. The locator is thus updated with the latest snapshot environment which allows the locator to see the change made by the previous SQL UPDATE statement. Therefore, in the next DBMS_LOB.READ, an error is returned because the LOB value is empty, that is, it does not contain any data.

INSERT INTO Print_media VALUES (3247, 20010, EMPTY_BLOB(),
'abcd', EMPTY_CLOB(), EMPTY_CLOB(), NULL, NULL, NULL, NULL);

COMMIT;

DECLARE
num_var           INTEGER;
clob_selected     CLOB;
read_amount       INTEGER;
read_offset       INTEGER;
buffer            VARCHAR2(20);

BEGIN

-- At time t1:
SELECT ad_sourcetext INTO clob_selected
FROM Print_media
WHERE ad_id = 20010;

read_amount := 10;
read_offset := 1;
dbms_lob.read(clob_selected, read_amount, read_offset, buffer);
dbms_output.put_line('clob_selected value: ' || buffer);
-- Produces the output 'abcd'

-- At time t2:
UPDATE Print_media SET ad_sourcetext = empty_clob()
WHERE ad_id = 20010;
-- although the most current current LOB value is now empty,
-- clob_selected still sees the LOB value as of the point
-- in time of the SELECT

read_amount := 10;
dbms_lob.read(clob_selected, read_amount, read_offset, buffer);
dbms_output.put_line('clob_selected value: ' || buffer);
-- Produces the output 'abcd'

-- At time t3:
SELECT ad_sourcetext INTO clob_selected FROM Print_media WHERE
ad_id = 20010;
-- the SELECT allows clob_selected to see the most current
-- LOB value

read_amount := 10;
dbms_lob.read(clob_selected, read_amount, read_offset, buffer);
-- ERROR: ORA-01403: no data found
END;
/

Example of Using One Locator to Update the Same LOB Value

Note:

Avoid updating the same LOB with different locators. You will avoid many pitfalls if you use only one locator to update a given LOB value.

In the following example, using table Print_media, two CLOBs are created as potential locators:

- clob_updated

- clob_copied

Note these progressions in the example at times t1 through t5:

- At the time of the first SELECT INTO (at t1), the value in ad_sourcetext is associated with the locator clob_updated.

- The second operation (at time t2) copies the value in clob_updated to clob_copied. At this time, both locators see the same value. The example demonstrates this with a series of DBMS_LOB.READ calls.

- At time t3, the program uses DBMS_LOB.WRITE to alter the value in clob_updated, and a DBMS_LOB.READ reveals a new value.

- However, a DBMS_LOB.READ of the value through clob_copied (at time t4) reveals that it still sees the value of the LOB as of the point in time of the assignment from clob_updated (at t2).

- It is not until clob_updated is assigned to clob_copied (t5) that clob_copied sees the modification made by clob_updated.

INSERT INTO PRINT_MEDIA VALUES (2049, 20030, EMPTY_BLOB(),
'abcd', EMPTY_CLOB(), EMPTY_CLOB(), NULL, NULL, NULL, NULL);

COMMIT;

DECLARE
num_var          INTEGER;
clob_updated     CLOB;
clob_copied      CLOB;
read_amount      INTEGER;
read_offset      INTEGER;
write_amount     INTEGER;
write_offset     INTEGER;
buffer           VARCHAR2(20);
BEGIN

-- At time t1:
SELECT ad_sourcetext INTO clob_updated FROM PRINT_MEDIA
WHERE ad_id = 20030
FOR UPDATE;

-- At time t2:
clob_copied := clob_updated;
-- after the assign, clob_copied and clob_updated see the same
-- LOB value

read_amount := 10;
read_offset := 1;
dbms_lob.read(clob_updated, read_amount, read_offset, buffer);
dbms_output.put_line('clob_updated value: ' || buffer);
-- Produces the output 'abcd'

read_amount := 10;
dbms_lob.read(clob_copied, read_amount, read_offset, buffer);
dbms_output.put_line('clob_copied value: ' || buffer);
-- Produces the output 'abcd'

-- At time t3:
write_amount := 3;
write_offset := 5;
buffer := 'efg';
dbms_lob.write(clob_updated, write_amount, write_offset,
buffer);

read_amount := 10;
dbms_lob.read(clob_updated, read_amount, read_offset, buffer);
dbms_output.put_line('clob_updated value: ' || buffer);
-- Produces the output 'abcdefg'

-- At time t4:
read_amount := 10;
dbms_lob.read(clob_copied, read_amount, read_offset, buffer);
dbms_output.put_line('clob_copied value: ' || buffer);
-- Produces the output 'abcd'

-- At time t5:
clob_copied := clob_updated;

read_amount := 10;
dbms_lob.read(clob_copied, read_amount, read_offset, buffer);
dbms_output.put_line('clob_copied value: ' || buffer);
-- Produces the output 'abcdefg'
END;
/

Example of Updating a LOB with a PL/SQL (DBMS_LOB) Bind Variable

When a LOB locator is used as the source to update another persistent LOB (as in a SQL INSERT or UPDATE statement, the DBMS_LOB.COPY routine, and so on), the snapshot environment in the source LOB locator determines the LOB value that is used as the source. If the source locator (for example L1) is a read consistent locator, then the LOB value as of the point in time of the SELECT of L1 is used. If the source locator (for example L2) is an updated locator, then the LOB value associated with the L2 snapshot environment at the time of the operation is used.

In the following example, using the table Print_media, three CLOBs are created as potential locators:

- clob_selected

- clob_updated

- clob_copied

Note these progressions in the example at times t1 through t5:

- At the time of the first SELECT INTO (at t1), the value in ad_sourcetext is associated with the locator clob_updated.

- The second operation (at t2) copies the value in clob_updated to clob_copied. At this juncture, both locators see the same value.

- Then (at t3), the program uses DBMS_LOB.WRITE to alter the value in clob_updated, and a DBMS_LOB.READ reveals a new value.

- However, a DBMS_LOB.READ of the value through clob_copied (at t4) reveals that clob_copied does not see the change made by clob_updated.

- Therefore (at t5), when clob_copied is used as the source for the value of the INSERT statement, the value associated with clob_copied (for example, without the new changes made by clob_updated) is inserted. This is demonstrated by the subsequent DBMS_LOB.READ of the value just inserted.

INSERT INTO PRINT_MEDIA VALUES (2056, 20020, EMPTY_BLOB(),
'abcd', EMPTY_CLOB(), EMPTY_CLOB(), NULL, NULL, NULL, NULL);

COMMIT;

DECLARE
num_var           INTEGER;
clob_selected     CLOB;
clob_updated      CLOB;
clob_copied       CLOB;
read_amount       INTEGER;
read_offset       INTEGER;
write_amount      INTEGER;
write_offset      INTEGER;
buffer            VARCHAR2(20);
BEGIN

-- At time t1:
SELECT ad_sourcetext INTO clob_updated FROM PRINT_MEDIA
WHERE ad_id = 20020
FOR UPDATE;

read_amount := 10;
read_offset := 1;
dbms_lob.read(clob_updated, read_amount, read_offset, buffer);
dbms_output.put_line('clob_updated value: ' || buffer);
-- Produces the output 'abcd'

-- At time t2:
clob_copied := clob_updated;

-- At time t3:
write_amount := 3;
write_offset := 5;
buffer := 'efg';
dbms_lob.write(clob_updated, write_amount, write_offset, buffer);

read_amount := 10;
dbms_lob.read(clob_updated, read_amount, read_offset, buffer);
dbms_output.put_line('clob_updated value: ' || buffer);
-- Produces the output 'abcdefg'
-- note that clob_copied does not see the write made before
-- clob_updated

-- At time t4:
read_amount := 10;
dbms_lob.read(clob_copied, read_amount, read_offset, buffer);
dbms_output.put_line('clob_copied value: ' || buffer);
-- Produces the output 'abcd'

-- At time t5:
-- the insert uses clob_copied view of the LOB value which does
-- not include clob_updated changes
INSERT INTO PRINT_MEDIA VALUES (2056, 20022, EMPTY_BLOB(),
clob_copied, EMPTY_CLOB(), EMPTY_CLOB(), NULL, NULL, NULL, NULL)
RETURNING ad_sourcetext INTO clob_selected;

read_amount := 10;
dbms_lob.read(clob_selected, read_amount, read_offset, buffer);
dbms_output.put_line('clob_selected value: ' || buffer);
-- Produces the output 'abcd'
END;
/

LOB Locators and Transaction Boundaries

This section discusses the use of LOB locators in transactions and transaction IDs. A basic description of LOB locators and their operations is given in "LOB Locators and BFILE Locators".

Note the following regarding LOB locators and transactions:

- Locators contain transaction IDs when:

You Begin the Transaction, Then Select Locator. If you begin a transaction and subsequently select a locator, then the locator contains the transaction ID. Note that you can implicitly be in a transaction without explicitly beginning one. For example, SELECT... FOR UPDATE implicitly begins a transaction. In such a case, the locator will contain a transaction ID.

- Locators Do Not Contain Transaction IDs When...

- You are Outside the Transaction, Then Select Locator. By contrast, if you select a locator outside of a transaction, then the locator does not contain a transaction ID.

- When Selected Prior to DML Statement Execution. A transaction ID will not be assigned until the first DML statement executes. Therefore, locators that are selected prior to such a DML statement will not contain a transaction ID.

Reading and Writing to a LOB Using Locators

You can always read the LOB data using the locator irrespective of whether the locator contains a transaction ID.

- Cannot Write Using Locator: If the locator contains a transaction ID, then you cannot write to the LOB outside of that particular transaction.

- Can Write Using Locator: If the locator does not contain a transaction ID, then you can write to the LOB after beginning a transaction either explicitly or implicitly.

- Cannot Read or Write Using Locator With Serializable Transactions: If the locator contains a transaction ID of an older transaction, and the current transaction is serializable, then you cannot read or write using that locator.

- Can Read, Not Write Using Locator With Non-Serializable Transactions: If the transaction is non-serializable, then you can read, but not write outside of that transaction.

The following examples show the relationship between locators and non-serializable transactions

Selecting the Locator Outside of the Transaction Boundary

The following scenarios describe techniques for using locators in non-serializable transactions when the locator is selected outside of a transaction.

Scenario:

1. Select the locator with no current transaction. At this point, the locator does not contain a transaction id.

2. Begin the transaction.

3. Use the locator to read data from the LOB.

4. Commit or rollback the transaction.

5. Use the locator to read data from the LOB.

6. Begin a transaction. The locator does not contain a transaction id.

7. Use the locator to write data to the LOB. This operation is valid because the locator did not contain a transaction id prior to the write. After this call, the locator contains a transaction id.

Scenario:

1. Select the locator with no current transaction. At this point, the locator does not contain a transaction id.

2. Begin the transaction. The locator does not contain a transaction id.

3. Use the locator to read data from the LOB. The locator does not contain a transaction id.

4. Use the locator to write data to the LOB. This operation is valid because the locator did not contain a transaction id prior to the write. After this call, the locator contains a transaction id. You can continue to read from or write to the LOB.

5. Commit or rollback the transaction. The locator continues to contain the transaction id.

6. Use the locator to read data from the LOB. This is a valid operation.

7. Begin a transaction. The locator already contains the previous transaction id.

8. Use the locator to write data to the LOB. This write operation will fail because the locator does not contain the transaction id that matches the current transaction.

Selecting the Locator Within a Transaction Boundary

The following scenarios describe techniques for using locators in non-serializable transactions when the locator is selected within a transaction.

Scenario:

1. Select the locator within a transaction. At this point, the locator contains the transaction id.

2. Begin the transaction. The locator contains the previous transaction id.

3. Use the locator to read data from the LOB. This operation is valid even though the transaction id in the locator does not match the current transaction.

See Also:

"Read Consistent Locators" for more information about using the locator to read LOB data.

4. Use the locator to write data to the LOB. This operation fails because the transaction id in the locator does not match the current transaction.

Scenario:

1. Begin a transaction.

2. Select the locator. The locator contains the transaction id because it was selected within a transaction.

3. Use the locator to read from or write to the LOB. These operations are valid.

4. Commit or rollback the transaction. The locator continues to contain the transaction id.

5. Use the locator to read data from the LOB. This operation is valid even though there is a transaction id in the locator and the transaction was previously committed or rolled back.

See Also:

"Read Consistent Locators" for more information on the using the locator to read LOB data.

6. Use the locator to write data to the LOB. This operation fails because the transaction id in the locator is for a transaction that was previously committed or rolled back.

LOB Locators Cannot Span Transactions

Modifying a persistent LOB value through the LOB locator using DBMS_LOB, OCI, or SQL INSERT or UPDATE statements changes the locator from a read consistent locator to an updated locator. The INSERT or UPDATE statement automatically starts a transaction and locks the row. Once this has occurred, the locator cannot be used outside the current transaction to modify the LOB value. In other words, LOB locators that are used to write data cannot span transactions. However, the locator can be used to read the LOB value unless you are in a serializable transaction.

See Also:

"LOB Locators and Transaction Boundaries", for more information about the relationship between LOBs and transaction boundaries.

In the following example, a CLOB locator is created: clob_updated

- At the time of the first SELECT INTO (at t1), the value in ad_sourcetext is associated with the locator clob_updated.

- The second operation (at t2), uses the DBMS_LOB.WRITE function to alter the value in clob_updated, and a DBMS_LOB.READ reveals a new value.

- The commit statement (at t3) ends the current transaction.

- Therefore (at t4), the subsequent DBMS_LOB.WRITE operation fails because the clob_updated locator refers to a different (already committed) transaction. This is noted by the error returned. You must re-select the LOB locator before using it in further DBMS_LOB (and OCI) modify operations.

Example of Locator Not Spanning a Transaction

INSERT INTO PRINT_MEDIA VALUES (2056, 20010, EMPTY_BLOB(),
'abcd', EMPTY_CLOB(), EMPTY_CLOB(), NULL, NULL, NULL, NULL);

COMMIT;

DECLARE
num_var          INTEGER;
clob_updated     CLOB;
read_amount      INTEGER;
read_offset      INTEGER;
write_amount     INTEGER;
write_offset     INTEGER;
buffer           VARCHAR2(20);

BEGIN
-- At time t1:
SELECT      ad_sourcetext
INTO        clob_updated
FROM        PRINT_MEDIA
WHERE       ad_id = 20010
FOR UPDATE;
read_amount := 10;
read_offset := 1;
dbms_lob.read(clob_updated, read_amount, read_offset, buffer);
dbms_output.put_line('clob_updated value: ' || buffer);
-- This produces the output 'abcd'

-- At time t2:
write_amount := 3;
write_offset := 5;
buffer := 'efg';
dbms_lob.write(clob_updated, write_amount, write_offset, buffer);
read_amount := 10;
dbms_lob.read(clob_updated, read_amount, read_offset, buffer);
dbms_output.put_line('clob_updated value: ' || buffer);
-- This produces the output 'abcdefg'

-- At time t3:
COMMIT;

-- At time t4:
dbms_lob.write(clob_updated , write_amount, write_offset, buffer);
-- ERROR: ORA-22990: LOB locators cannot span transactions
END;
/

LOBs in the Object Cache

Consider these object cache issues for internal and external LOB attributes:

- Persistent LOB attributes: Creating an object in object cache, sets the LOB attribute to empty.

When you create an object in the object cache that contains a persistent LOB attribute, the LOB attribute is implicitly set to empty. You may not use this empty LOB locator to write data to the LOB. You must first flush the object, thereby inserting a row into the table and creating an empty LOB — that is, a LOB with 0 length. Once the object is refreshed in the object cache (use OCI_PIN_LATEST), the real LOB locator is read into the attribute, and you can then call the OCI LOB API to write data to the LOB.

- External LOB (BFILE) attributes: Creating an object in object cache, sets the BFILE attribute to NULL.

When creating an object with an external LOB (BFILE) attribute, the BFILE is set to NULL. It must be updated with a valid directory object name and file name before reading from the BFILE.

When you copy one object to another in the object cache with a LOB locator attribute, only the LOB locator is copied. This means that the LOB attribute in these two different objects contain exactly the same locator which refers to one and the same LOB value. Only when the target object is flushed is a separate, physical copy of the LOB value made, which is distinct from the source LOB value.

See Also:

"Example of Updating LOBs and Read-Consistency" for a description of what version of the LOB value will be seen by each object if a write is performed through one of the locators.

Therefore, in cases where you want to modify the LOB that was the target of the copy, you must flush the target object, refresh the target object, and then write to the LOB through the locator attribute.

Terabyte-Size LOB Support

Terabyte-size LOBs—LOBs up to a maximum size of 8 to 128 terabytes depending on your database block size—are supported by the following APIs:

- Java using JDBC (Java Database Connectivity)

- PL/SQL using the DBMS_LOB Package

- C using OCI (Oracle Call Interface)

You cannot create and use LOB instances of size greater than 4 gigabytes —"terabyte-size LOBs"— in the following programmatic environments:

- COBOL using the Pro*COBOL Precompiler

- C or C++ using the Pro*C/C++ Precompiler

- Visual Basic using OO4O (Oracle Objects for OLE)

Note:

Oracle Database does not support BFILEs larger than 2^64-1 bytes (UB8MAXVAL in OCI) in any programmatic environment. Any additional file size limit imposed by your operating system also applies to BFILEs.

Maximum Storage Limit for Terabyte-Size LOBs

In supported environments, you can create and manipulate LOBs that are up to the maximum storage size limit for your database configuration.

Oracle Database lets you create tablespaces with block sizes different from the database block size, and the maximum size of a LOB depends on the size of the tablespace blocks. CHUNK is a parameter of LOB storage whose value is controlled by the block size of the tablespace in which the LOB is stored.

When you create a LOB column, you can specify a value for CHUNK, which is the number of bytes to be allocated for LOB manipulation. The value must be a multiple of the tablespace block size, or Oracle Database rounds up to the next multiple. (If the tablespace block size is the same as the database block size, then CHUNK is also a multiple of the database block size.)

The maximum allowable storage limit for your configuration depends on the tablespace block size setting, and is calculated as (4 gigabytes - 1) times the value obtained from DBMS_LOB.GETCHUNKSIZE or OCILobGetChunkSize(). This value, in number of bytes for BLOBs or number of characters for CLOBs, is actually less than the size of the CHUNK parameter due to internal storage overhead. With the current allowable range for the tablespace block size from 2K to 32K, the storage limit ranges from 8 terabytes to 128 terabytes.

For example, suppose your database block size is 32K bytes and you create a tablespace with a nonstandard block size of 8K. Further suppose that you create a table with a LOB column and specify a CHUNK size of 16K (which is a multiple of the 8K tablespace block size). Then the maximum size of a LOB in this column is (4 gigabytes - 1) * 16K.

See Also:

- Oracle Database Administrator's Guide for details on the initialization parameter setting for your database installation.

- "CHUNK"

This storage limit applies to all LOB types in environments that support terabyte-size LOBs. However, note that CLOB and NCLOB types are sized in characters, while the BLOB type is sized in bytes.

Using Terabyte-Size LOBs with JDBC

You can use the LOB APIs included in the Oracle JDBC classes to access terabyte-size LOBs.

See Also:

"Using Java (JDBC) to Work with LOBs"

Using Terabyte-Size LOBs with the DBMS_LOB Package

You can access terabyte-size LOBs with all APIs in the DBMS_LOB PL/SQL package. Use DBMS_LOB.GETCHUNKSIZE to obtain the value to be used in reading and writing LOBs. The number of bytes stored in a chunk is actually less than the size of the CHUNK parameter due to internal storage overhead. The DBMS_LOB.GET_STORAGE_LIMIT function returns the storage limit for your database configuration. This is the maximum allowable size for LOBs. BLOBs are sized in bytes, while CLOBs and NCLOBs are sized in characters.

See Also:

Oracle Database PL/SQL Packages and Types Reference for details on the initialization parameter setting for your database installation.

Using Terabyte-Size LOBs with OCI

The Oracle Call Interface API provides a set of functions for operations on LOBs of all sizes. OCILobGetChunkSize() returns the value, in bytes for BLOBs, or in characters for CLOBs, to be used in reading and writing LOBs. For varying-width character sets, the value is the number of Unicode characters that fit. The number of bytes stored in a chunk is actually less than the size of the CHUNK parameter due to internal storage overhead. The function OCILobGetStorageLimit() returns the maximum allowable size, in bytes, of internal LOBs in the current database installation. If streaming mode is used, where the whole LOB is read, there is no need to get the chunk size.

See Also:

Oracle Call Interface Programmer's Guide, the chapter "LOB and BFILE Operations", section "Using LOBs of Size Greater than 4GB" for details on OCI functions that support LOBs.

Guidelines for Creating Gigabyte LOBs

To create gigabyte LOBs in supported environments, use the following guidelines to make use of all available space in the tablespace for LOB storage:

- Single Data File Size Restrictions: There are restrictions on the size of a single data file for each operating system. For example, Solaris 2.5 only allows operating system files of up to 2 gigabytes. Hence, add more data files to the tablespace when the LOB grows larger than the maximum allowed file size of the operating system on which your Oracle Database runs.

- Set PCT INCREASE Parameter to Zero: PCTINCREASE parameter in the LOB storage clause specifies the percent growth of the new extent size. When a LOB is being filled up piece by piece in a tablespace, numerous new extents get created in the process. If the extent sizes keep increasing by the default value of 50 percent every time, then extents will become unmanageable and eventually will waste unnecessary space in the tablespace. Therefore, the PCTINCREASE parameter should be set to zero or a small value.

- Set MAXEXTENTS to a Suitable Value or UNLIMITED: The MAXEXTENTS parameter limits the number of extents allowed for the LOB column. A large number of extents are created incrementally as the LOB size grows. Therefore, the parameter should be set to a value that is large enough to hold all the LOBs for the column. Alternatively, you could set it to UNLIMITED.

- Use a Large Extent Size: For every new extent created, Oracle generates undo information for the header and other metadata for the extent. If the number of extents is large, then the rollback segment can be saturated. To get around this, choose a large extent size, say 100 megabytes, to reduce the frequency of extent creation, or commit the transaction more often to reuse the space in the rollback segment.

Creating a Tablespace and Table to Store Gigabyte LOBs

The following example illustrates how to create a tablespace and table to store gigabyte LOBs.

CREATE TABLESPACE lobtbs1 DATAFILE '/your/own/data/directory/lobtbs_1.dat'
SIZE 2000M REUSE ONLINE NOLOGGING DEFAULT STORAGE (MAXEXTENTS UNLIMITED);
ALTER TABLESPACE lobtbs1 ADD DATAFILE
'/your/own/data/directory/lobtbs_2.dat' SIZE 2000M REUSE;

CREATE TABLE print_media_backup
(product_id NUMBER(6),
ad_id NUMBER(6),
ad_composite BLOB,
ad_sourcetext CLOB,
ad_finaltext CLOB,
ad_fltextn NCLOB,
ad_textdocs_ntab textdoc_tab,
ad_photo BLOB,
ad_graphic BLOB,
ad_header adheader_typ)
NESTED TABLE ad_textdocs_ntab STORE AS textdocs_nestedtab5
LOB(ad_sourcetext) STORE AS (TABLESPACE lobtbs1 CHUNK 32768 PCTVERSION 0
NOCACHE NOLOGGING
STORAGE(INITIAL 100M NEXT 100M MAXEXTENTS
UNLIMITED PCTINCREASE 0));

Note the following with respect to this example:

- The storage clause in this example is specified in the CREATE TABLESPACE statement.

- You can specify the storage clause in the CREATE TABLE statement as an alternative.

- The storage clause is not allowed in the CREATE TEMPORARY TABLESPACE statement.

- Setting the PCTINCREASE parameter to 0 is recommended for gigabyte LOBs. For small, or medium size lobs, the default PCTINCREASE value of 50 is recommended as it reduces the number of extent allocations.

6 Overview of Supplied LOB APIs

This chapter contains these topics:

- Programmatic Environments That Support LOBs

- Comparing the LOB Interfaces

- Using PL/SQL (DBMS_LOB Package) to Work with LOBs

- Using OCI to Work with LOBs

- Using C++ (OCCI) to Work with LOBs

- Using C/C++ (Pro*C) to Work with LOBs

- Using COBOL (Pro*COBOL) to Work with LOBs

- Using Visual Basic (Oracle Objects for OLE) to Work with LOBs

- Using Java (JDBC) to Work with LOBs

- Oracle Provider for OLE DB (OraOLEDB)

- Overview of Oracle Data Provider for .NET (ODP.NET)

Programmatic Environments That Support LOBs

Table 6-1 lists the programmatic environments that support LOB functionality.

See Also:

APIs for supported LOB operations are described in detail in:

- Chapter 12, "Operations Specific to Persistent and Temporary LOBs"

- Chapter 14, " LOB APIs for Basic Operations"

- Chapter 15, "LOB APIs for BFILE Operations"

Table 6-1 Programmatic Environments That Support LOBs

Language

Precompiler or Interface Program

Syntax Reference

In This Chapter See...

PL/SQL

DBMS_LOB Package

Oracle Database PL/SQL Packages and Types Reference

"Using PL/SQL (DBMS_LOB Package) to Work with LOBs".

C

Oracle Call Interface for C (OCI)

Oracle Call Interface Programmer's Guide

"Using OCI to Work with LOBs".

C++

Oracle Call Interface for C++ (OCCI)

Oracle C++ Call Interface Programmer's Guide

"Using C++ (OCCI) to Work with LOBs" .

C/C++

Pro*C/C++ Precompiler

Pro*C/C++ Programmer's Guide

"Using C/C++ (Pro*C) to Work with LOBs".

COBOL

Pro*COBOL Precompiler

Pro*COBOL Programmer's Guide

"Using COBOL (Pro*COBOL) to Work with LOBs".

Visual Basic

Oracle Objects For OLE (OO4O)

Oracle Objects for OLE (OO4O) is a Windows-based product included with the database.
There are no manuals for this product, only online help. Online help is available through the Application Development submenu of the database installation.

"Using Visual Basic (Oracle Objects for OLE) to Work with LOBs"."

Java

JDBC Application Programmatic Interface (API)

Oracle Database JDBC Developer's Guide and Reference.

"Using Java (JDBC) to Work with LOBs".

OLEDB

OraOLEDB, an OLE DB provider for Oracle.

Oracle Provider for OLE DB Developer's Guide

"Oracle Provider for OLE DB (OraOLEDB)"

Comparing the LOB Interfaces

Table 6-2 and Table 6-3 compare the eight LOB programmatic interfaces by listing their functions and methods used to operate on LOBs. The tables are split in two simply to accommodate all eight interfaces. The functionality of the interfaces, with regards to LOBs, is described in the following sections.

Table 6-2 Comparing the LOB Interfaces, 1 of 2

PL/SQL: DBMS_LOB (dbmslob.sql)

C (OCI)(ociap.h)

C++ (OCCI) (occiData.h). Also for Clob and Bfile classes.

Pro*C/C++ and Pro*COBOL

DBMS_LOB.COMPARE

N/A

N/A

N/A

DBMS_LOB.INSTR

N/A

N/A

N/A

DBMS_LOB.SUBSTR

N/A

N/A

N/A

DBMS_LOB.APPEND

OCILobAppend()

Blob.append()

APPEND

N/A (use PL/SQL assign operator)

OCILobAssign()

ASSIGN

N/A

OCILobCharSetForm()

Clob.getCharsetForm (CLOB only)

N/A

N/A

OCILobCharSetId()

Clob.getCharsetId()

(CLOB only)

N/A

DBMS_LOB.CLOSE

OCILobClose()

Blob.close()

CLOSE

N/A

N/A

Clob.closeStream()

N/A

DBMS_LOB.COPY

OCILobCopy2()

Blob.copy()

COPY

N/A

OCILobDisableBuffering()

N/A

DISABLE BUFFERING

N/A

OCILobEnableBuffering()

N/A

ENABLE BUFFERING

DBMS_LOB.ERASE

OCILobErase2()

N/A

ERASE

DBMS_LOB.FILECLOSE

OCILobFileClose()

Clob.close()

CLOSE

DBMS_LOB.FILECLOSEALL

OCILobFileCloseAll()

N/A

FILE CLOSE ALL

DBMS_LOB.FILEEXISTS

OCILobFileExist()

Bfile.fileExists()

DESCRIBE [FILEEXISTS]

DBMS_LOB.GETCHUNKSIZE

OCILobGetChunkSize()

Blob.getChunkSize()

DESCRIBE [CHUNKSIZE]

DBMS_LOB.FILEGETNAME

OCILobFileGetName()

Bfile.getFileName() and Bfile.getDirAlias()

DESCRIBE [DIRECTORY, FILENAME]

DBMS_LOB.FILEISOPEN

OCILobFileIsOpen()

Bfile.isOpen()

DESCRIBE [ISOPEN]

DBMS_LOB.FILEOPEN

OCILobFileOpen()

Bfile.open()

OPEN

N/A (use BFILENAME operator)

OCILobFileSetName()

Bfile.setName()

FILE SET

N/A

OCILobFlushBuffer()

N/A

FLUSH BUFFER

DBMS_LOB.GETLENGTH

OCILobGetLength2()

Blob.length()

DESCRIBE [LENGTH]

N/A

OCILobIsEqual()

Use operator = ( )=/!=

N/A

DBMS_LOB.ISOPEN

OCILobIsOpen()

Blob.isOpen()

DESCRIBE [ISOPEN]

DBMS_LOB.LOADFROMFILE

OCILobLoadFromFile2()

Use the overloadedcopy() method.

LOAD FROM FILE

N/A

OCILobLocatorIsInit()

Clob.isinitialized()

N/A

DBMS_LOB.OPEN

OCILobOpen()

Blob.open

OPEN

DBMS_LOB.READ

OCILobRead()

Blob.read

READ

DBMS_LOB.TRIM

OCILobTrim2()

Blob.trim

TRIM

DBMS_LOB.WRITE

OCILobWrite2

Blob.write

WRITEORALOB.

DBMS_LOB.WRITEAPPEND

OCILobWriteAppend2()

N/A

WRITE APPEND

DBMS_LOB.CREATETEMPORARY

OCILobCreateTemporary()

N/A

N/A

DBMS_LOB.FREETEMPORARY

OCILobFreeTemporary()

N/A

N/A

DBMS_LOB.ISTEMPORARY

OCILobIsTemporary()

N/A

N/A

N/A

OCILobLocatorAssign()

use operator = ( ) or copy constructor

N/A

Table 6-3 Comparing the LOB Interfaces, 2 of 2

PL/SQL: DBMS_LOB (dbmslob.sql)

Visual Basic (OO4O)

Java (JDBC

OLEDB

DBMS_LOB.COMPARE

ORALOB.Compare

Use DBMS_LOB.

N/A

DBMS_LOB.INSTR

ORALOB.Matchpos

position

N/A

DBMS_LOB.SUBSTR

N/A

getBytes for BLOBs or BFILEs

getSubString for CLOBs

N/A

DBMS_LOB.APPEND

ORALOB.Append

Use length and then putBytes or PutString

N/A

N/A [use PL/SQL assign operator]

ORALOB.Clone

N/A [use equal sign]

N/A

N/A

N/A

N/A

N/A

N/A

N/A

N/A

N/A

DBMS_LOB.CLOSE

N/A

use DBMS_LOB.

N/A

DBMS_LOB.COPY

ORALOB.Copy

Use read and write

N/A

N/A

ORALOB.DisableBuffering

N/A

N/A

N/A

ORALOB.EnableBuffering

N/A

N/A

DBMS_LOB.ERASE

ORALOB.Erase

Use DBMS_LOB.

N/A

DBMS_LOB.FILECLOSE

ORABFILE.Close

closeFile

N/A

DBMS_LOB.FILECLOSEALL

ORABFILE.CloseAll

Use DBMS_LOB.

N/A

DBMS_LOB.FILEEXISTS

ORABFILE.Exist

fileExists

N/A

DBMS_LOB.GETCHUNKSIZE

N/A

getChunkSize

N/A

DBMS_LOB.FILEGETNAME

ORABFILE.DirectoryName

ORABFILE.FileName

getDirAlias

getName

N/A

DBMS_LOB.FILEISOPEN

ORABFILE.IsOpen

Use DBMS_LOB.ISOPEN

N/A

DBMS_LOB.FILEOPEN

ORABFILE.Open

openFile

N/A

N/A (use BFILENAME operator)

DirectoryName

FileName

Use BFILENAME

N/A

N/A

ORALOB.FlushBuffer

N/A

N/A

DBMS_LOB.GETLENGTH

ORALOB.Size

length

N/A

N/A

N/A

equals

N/A

DBMS_LOB.ISOPEN

ORALOB.IsOpen

use DBMS_LOB. IsOpen

N/A

DBMS_LOB.LOADFROMFILE

ORALOB.

CopyFromBfile

Use read and then write

N/A

DBMS_LOB.OPEN

ORALOB.open

Use DBMS_LOB.

N/A

DBMS_LOB.READ

ORALOB.Read

BLOB or BFILE: getBytes and getBinaryStream
CLOB: getString and getSubString and getCharacterStream

IRowset::GetData and ISequentialStream::Read

DBMS_LOB.TRIM

ORALOB.Trim

Use DBMS_LOB.

N/A

DBMS_LOB.WRITE

ORALOB.Write

BLOB: setBytes and setBinaryStream
CLOB: setString and setCharacterStream

IRowsetChange::SetData

and

ISequentialStream::Write

DBMS_LOB.WRITEAPPEND

N/A

Use length and then putString or putBytes

N/A

DBMS_LOB.CREATETEMPORARY

N/A

N/A

N/A

DBMS_LOB.FREETEMPORARY

N/A

N/A

N/A

DBMS_LOB.ISTEMPORARY

N/A

N/A

N/A

Using PL/SQL (DBMS_LOB Package) to Work with LOBs

The PL/SQL DBMS_LOB package can be used for the following operations:

- Internal persistent LOBs and Temporary LOBs: Read and modify operations, either entirely or in a piece-wise manner.

- BFILEs: Read operations

See Also:

Oracle Database PL/SQL Packages and Types Reference for detailed documentation, including parameters, parameter types, return values, and example code.

Provide a LOB Locator Before Running the DBMS_LOB Routine

As described in more detail in the following, DBMS_LOB routines work based on LOB locators. For the successful completion of DBMS_LOB routines, you must provide an input locator representing a LOB that exists in the database tablespaces or external file system, before you call the routine.

- Persistent LOBs: First use SQL to define tables that contain LOB columns, and subsequently you can use SQL to initialize or populate the locators in these LOB columns.

- External LOBs: Define a DIRECTORY object that maps to a valid physical directory containing the external LOBs that you intend to access. These files must exist, and have READ permission for Oracle Server to process. If your operating system uses case-sensitive path names, then specify the directory in the correct case. See "Directory Objects" for more information.

Once the LOBs are defined and created, you may then SELECT a LOB locator into a local PL/SQL LOB variable and use this variable as an input parameter to DBMS_LOB for access to the LOB value.

Examples provided with each DBMS_LOB routine will illustrate this in the following sections.

Guidelines for Offset and Amount Parameters in DBMS_LOB Operations

The following guidelines apply to offset and amount parameters used in procedures in the DBMS_LOB PL/SQL package:

- For character data—in all formats, fixed-width and varying-width—the amount and offset parameters are in characters. This applies to operations on CLOB and NCLOB datatypes.

- For binary data, the offset and amount parameters are in bytes. This applies to operations on BLOB datatypes.

- When using the following procedures:

- DBMS_LOB.LOADFROMFILE

- DBMS_LOB.LOADBLOBFROMFILE

- DBMS_LOB.LOADCLOBFROMFILE

you cannot specify an amount parameter with a value larger than the size of the BFILE you are loading from. To load the entire BFILE with these procedures, you must specify either the exact size of the BFILE, or the maximum allowable storage limit.

See Also:

- "Loading a LOB with Data from a BFILE"

- "Loading a BLOB with Data from a BFILE"

- "Loading a CLOB or NCLOB with Data from a BFILE"

- When using DBMS_LOB.READ, the amount parameter can be larger than the size of the data. The amount should be less than or equal to the size of the buffer. The buffer size is limited to 32K.

See Also:

"Reading Data from a LOB"

Determining Character Set ID

To determine the character set ID, you must know the character set name (a user can select from the V$NLS_VALID_VALUES view, which lists the names of the character sets that are valid as database and national character sets). Then call the function NLS_CHARSET_ID with the desired character set name as the one string argument. The character set ID is returned as an integer. UTF16 does not work because it has no character set name. Use character set ID = 1000 for UTF16. Although UTF16 is not allowed as a database or national character set, the APIs in DBMS_LOB support it for database conversion purposes. DBMS_LOB.LOADCLOBFROMFILE and other procedures in DBMS_LOB take character set ID, not character set name, as an input.

See Also:

Oracle Database Globalization Support Guide, Appendix A, for supported languages

PL/SQL Functions and Procedures for LOBs

PL/SQL functions and procedures that operate on BLOBs, CLOBs, NCLOBs, and BFILEs are summarized in the following:

- To modify persistent LOB values, see Table 6-4

- To read or examine LOB values, see Table 6-5

- To create, free, or check on temporary LOBs, see Table 6-6

- For read-only functions on external LOBs (BFILEs), see Table 6-7

- To open or close a LOB, or check if LOB is open, see Table 6-8

PL/SQL Functions and Procedures to Modify LOB Values

Table 6-4 PL/SQL: DBMS_LOB Procedures to Modify LOB Values

Function/Procedure

Description

APPEND

Appends the LOB value to another LOB

CONVERTTOBLOB

Converts a CLOB to a BLOB

CONVERTTOCLOB

Converts a BLOB to a CLOB

COPY

Copies all or part of a LOB to another LOB

ERASE

Erases part of a LOB, starting at a specified offset

LOADFROMFILE

Load BFILE data into a persistent LOB

LOADCLOBFROMFILE

Load character data from a file into a LOB

LOADBLOBFROMFILE

Load binary data from a file into a LOB

TRIM

Trims the LOB value to the specified shorter length

WRITE

Writes data to the LOB at a specified offset

WRITEAPPEND

Writes data to the end of the LOB

PL/SQL Functions and Procedures for Introspection of LOBs

Table 6-5 PL/SQL: DBMS_LOB Procedures to Read or Examine Internal and External LOB values

Function/Procedure

Description

COMPARE

Compares the value of two LOBs

GETCHUNKSIZE

Gets the chunk size used when reading and writing. This only works on persistent LOBs and does not apply to external LOBs (BFILEs).

GETLENGTH

Gets the length of the LOB value

INSTR

Returns the matching position of the nth occurrence of the pattern in the LOB

READ

Reads data from the LOB starting at the specified offset

SUBSTR

Returns part of the LOB value starting at the specified offset

PL/SQL Operations on Temporary LOBs

Table 6-6 PL/SQL: DBMS_LOB Procedures to Operate on Temporary LOBs

Function/Procedure

Description

CREATETEMPORARY

Creates a temporary LOB

ISTEMPORARY

Checks if a LOB locator refers to a temporary LOB

FREETEMPORARY

Frees a temporary LOB

PL/SQL Read-Only Functions and Procedures for BFILEs

Table 6-7 PL/SQL: DBMS_LOB Read-Only Procedures for BFILEs

Function/Procedure

Description

FILECLOSE

Closes the file. Use CLOSE() instead.

FILECLOSEALL

Closes all previously opened files

FILEEXISTS

Checks if the file exists on the server

FILEGETNAME

Gets the directory object name and file name

FILEISOPEN

Checks if the file was opened using the input BFILE locators. Use ISOPEN() instead.

FILEOPEN

Opens a file. Use OPEN() instead.

PL/SQL Functions and Procedures to Open and Close Internal and External LOBs

Table 6-8 PL/SQL: DBMS_LOB Procedures to Open and Close Internal and External LOBs

Function/Procedure

Description

OPEN

Opens a LOB

ISOPEN

Sees if a LOB is open

CLOSE

Closes a LOB

These procedures are described in detail for specific LOB operations, such as, INSERT a row containing a LOB, in "Opening Persistent LOBs with the OPEN and CLOSE Interfaces".

Using OCI to Work with LOBs

Oracle Call Interface (OCI) LOB APIs enable you to access and make changes to LOBs and read data from BFILEs in C. OCI functions for LOBs are discussed in greater detail later in this section.

Setting the CSID Parameter for OCI LOB APIs

If you want to read or write data in 2 byteUunicode (UCS2) format, then set the csid (character set ID) parameter in OCILobRead2() and OCILobWrite2() to OCI_UCS2ID. The csid parameter indicates the character set id for the buffer parameter. You can set the csid parameter to any character set ID. If the csid parameter is set, then it will override the NLS_LANG environment variable.

See Also:

- Oracle Call Interface Programmer's Guide for information on the OCIUnicodeToCharSet() function and details on OCI syntax in general.

- Oracle Database Globalization Support Guide for detailed information about implementing applications in different languages.

Fixed-Width and Varying-Width Character Set Rules for OCI

In OCI, for fixed-width client-side character sets, the following rules apply:

- CLOBs and NCLOBs: offset and amount parameters are always in characters

- BLOBs and BFILEs: offset and amount parameters are always in bytes

The following rules apply only to varying-width client-side character sets:

- Offset parameter: Regardless of whether the client-side character set is varying-width, the offset parameter is always as follows:

- CLOBs and NCLOBs: in characters

- BLOBs and BFILEs: in bytes

- Amount parameter: The amount parameter is always as follows:

- When referring to a server-side LOB: in characters

- When referring to a client-side buffer: in bytes

- OCILobFileGetLength(): Regardless of whether the client-side character set is varying-width, the output length is as follows:

- CLOBs and NCLOBs: in characters

- BLOBs and BFILEs: in bytes

- OCILobRead2(): With client-side character set of varying-width, CLOBs and NCLOBs:

- Input amount is in characters. Input amount refers to the number of characters to read from the server-side CLOB or NCLOB.

- Output amount is in bytes. Output amount indicates how many bytes were read into the buffer bufp.

- OCILobWrite2(): With client-side character set of varying-width, CLOBs and NCLOBs:

- Input amount is in bytes. The input amount refers to the number of bytes of data in the input buffer bufp.

- Output amount is in characters. The output amount refers to the number of characters written into the server-side CLOB or NCLOB.

Other Operations

For all other LOB operations, irrespective of the client-side character set, the amount parameter is in characters for CLOBs and NCLOBs. These include OCILobCopy2(), OCILobErase2(), OCILobLoadFromFile2(), and OCILobTrim2(). All these operations refer to the amount of LOB data on the server.

See also:

Oracle Database Globalization Support Guide

NCLOBs in OCI

NCLOBs are allowed as parameters in methods.

OCILobLoadFromFile2() Amount Parameter

When using OCILobLoadFromFile2() you cannot specify amount larger than the length of the BFILE. To load the entire BFILE, you can pass the value returned by OCILobGetStorageLimit().

OCILobRead2() Amount Parameter

To read to the end of a LOB using OCILobRead2(), you specify an amount equal to the value returned by OCILobGetStorageLimit(). See "Reading Data from a LOB" for more information.

OCILobLocator Pointer Assignment

Special care must be taken when assigning OCILobLocator pointers in an OCI program—using the "=" assignment operator. Pointer assignments create a shallow copy of the LOB. After the pointer assignment, the source and target LOBs point to the same copy of data.

These semantics are different from using LOB APIs, such as OCILobAssign() or OCILobLocatorAssign() to perform assignments. When the these APIs are used, the locators logically point to independent copies of data after assignment.

For temporary LOBs, before performing pointer assignments, you must ensure that any temporary LOB in the target LOB locator is freed by calling OCIFreeTemporary(). In contrast, when OCILobLocatorAssign() is used, the original temporary LOB in the target LOB locator variable, if any, is freed automatically before the assignment happens.

LOB Locators in Defines and Out-Bind Variables in OCI

Before you reuse a LOB locator in a define or an out-bind variable in a SQL statement, you must free any temporary LOB in the existing LOB locator buffer using OCIFreeTemporary().

OCI Functions That Operate on BLOBs, CLOBs, NCLOBs, and BFILEs

OCI functions that operate on BLOBs, CLOBs, NCLOBs, and BFILEs are as follows:

- To modify persistent LOBs, see Table 6-9

- To read or examine LOB values, see Table 6-10

- To create or free temporary LOB, or check if Temporary LOB exists, see Table 6-11

- For read only functions on external LOBs (BFILEs), see Table 6-12

- To operate on LOB locators, see Table 6-13

- For LOB buffering, see Table 6-14

- To open and close LOBs, see Table 6-15

OCI Functions to Modify Persistent LOB (BLOB, CLOB, and NCLOB) Values

Table 6-9 OCI Functions to Modify Persistent LOB (BLOB, CLOB, and NCLOB) Values

Function/Procedure

Description

OCILobArrayWrite()

Writes data using multiple locators in one round trip.

OCILobAppend()

Appends LOB value to another LOB.

OCILobCopy2()

Copies all or part of a LOB to another LOB.

OCILobErase2()

Erases part of a LOB, starting at a specified offset.

OCILobLoadFromFile2()

Loads BFILE data into a persistent LOB.

OCILobTrim2()

Truncates a LOB.

OCILobWrite2()

Writes data from a buffer into a LOB, overwriting existing data.

OCILobWriteAppend2()

Writes data from a buffer to the end of the LOB.

OCI Functions to Read or Examine Persistent LOB and External LOB (BFILE) Values

Table 6-10 OCI Functions to Read or Examine persistent LOB and external LOB (BFILE) Values

Function/Procedure

Description

OCILobArrayRead()

Reads data using multiple locators in one round trip.

OCILobGetChunkSize()

Gets the Chunk size used when reading and writing. This works on persistent LOBs and does not apply to external LOBs (BFILEs).

OCILobGetLength2()

Returns the length of a LOB or a BFILE.

OCILobRead2()

Reads a specified portion of a non-NULL LOB or a BFILE into a buffer.

OCI Functions for Temporary LOBs

Table 6-11 OCI Functions for Temporary LOBs

Function/Procedure

Description

OCILobCreateTemporary()

Creates a temporary LOB

OCILobIsTemporary()

Sees if a temporary LOB exists

OCILobFreeTemporary()

Frees a temporary LOB

OCI Read-Only Functions for BFILEs

Table 6-12 OCI Read-Only Functions for BFILES

Function/Procedure

Description

OCILobFileClose()

Closes an open BFILE.

OCILobFileCloseAll()

Closes all open BFILEs.

OCILobFileExists()

Checks whether a BFILE exists.

OCILobFileGetName()

Returns the name of a BFILE.

OCILobFileIsOpen()

Checks whether a BFILE is open.

OCILobFileOpen()

Opens a BFILE.

OCI LOB Locator Functions

Table 6-13 OCI LOB-Locator Functions

Function/Procedure

Description

OCILobAssign()

Assigns one LOB locator to another.

OCILobCharSetForm()

Returns the character set form of a LOB.

OCILobCharSetId()

Returns the character set ID of a LOB.

OCILobFileSetName()

Sets the name of a BFILE in a locator.

OCILobIsEqual()

Checks whether two LOB locators refer to the same LOB.

OCILobLocatorIsInit()

Checks whether a LOB locator is initialized.

OCI LOB-Buffering Functions

Table 6-14 OCI LOB-Buffering Functions

Function/Procedure

Description

OCILobDisableBuffering()

Disables the buffering subsystem use.

OCILobEnableBuffering()

Uses the LOB buffering subsystem for subsequent reads and writes of LOB data.

OCILobFlushBuffer()

Flushes changes made to the LOB buffering subsystem to the database (server)

OCI Functions to Open and Close Internal and External LOBs

Table 6-15 OCI Functions to Open and Close Internal and External LOBs

Function/Procedure

Description

OCILobOpen()

Opens a LOB

OCILobIsOpen()

Sees if a LOB is open

OCILobClose()

Closes a LOB

OCI LOB Examples

Further OCI examples are provided in:

- Chapter 14, " LOB APIs for Basic Operations"

- Chapter 15, "LOB APIs for BFILE Operations"

See also Appendix B, "OCI Demonstration Programs" in Oracle Call Interface Programmer's Guide, for further OCI demonstration script listings.

Further Information About OCI

For further information and features of OCI, refer to the OTN Web site, http://www.oracle.com/technology/ for OCI features and FAQs.

Using C++ (OCCI) to Work with LOBs

Oracle C++ Call Interface (OCCI) is a C++ API for manipulating data in an Oracle database. OCCI is organized as an easy-to-use set of C++ classes that enable a C++ program to connect to a database, run SQL statements, insert/update values in database tables, retrieve results of a query, run stored procedures in the database, and access metadata of database schema objects. OCCI also provides a seamless interface to manipulate objects of user-defined types as C++ class instances.

Oracle C++ Call Interface (OCCI) is designed so that you can use OCI and OCCI together to build applications.

The OCCI API provides the following advantages over JDBC and ODBC:

- OCCI encompasses more Oracle functionality than JDBC. OCCI provides all the functionality of OCI that JDBC does not provide.

- OCCI provides compiled performance. With compiled programs, the source code is already written as close to the computer as possible. Because JDBC is an interpreted API, it cannot provide the performance of a compiled API. With an interpreted program, performance degrades as each line of code must be interpreted individually into code that is close to the computer.

- OCCI provides memory management with smart pointers. You do not have to be concerned about managing memory for OCCI objects. This results in robust higher performance application code.

- Navigational access of OCCI enables you to intuitively access objects and call methods. Changes to objects persist without need to write corresponding SQL statements. If you use the client side cache, then the navigational interface performs better than the object interface.

- With respect to ODBC, the OCCI API is simpler to use. Because ODBC is built on the C language, OCCI has all the advantages C++ provides over C. Moreover, ODBC has a reputation as being difficult to learn. The OCCI, by contrast, is designed for ease of use.

You can use OCCI to make changes to an entire persistent LOB, or to pieces of the beginning, middle, or end of it, as follows:

- For reading from internal and external LOBs (BFILEs)

- For writing to persistent LOBs

OCCI Classes for LOBs

OCCI provides the following classes that allow you to use different types of LOB instances as objects in your C++ application:

- Clob class to access and modify data stored in internal CLOBs and NCLOBs

- Blob class to access and modify data stored in internal BLOBs

- Bfile class to access and read data stored in external LOBs (BFILEs)

See Also:

Syntax information on these classes and details on OCCI in general is available in the Oracle C++ Call Interface Programmer's Guide.

Clob Class

The Clob driver implements a CLOB object using an SQL LOB locator. This means that a CLOB object contains a logical pointer to the SQL CLOB data rather than the data itself.

The CLOB interface provides methods for getting the length of an SQL CLOB value, for materializing a CLOB value on the client, and getting a substring. Methods in the ResultSet and Statement interfaces such as getClob() and setClob() allow you to access SQL CLOB values.

See Also:

Oracle C++ Call Interface Programmer's Guide for detailed information on the Clob class.

Blob Class

Methods in the ResultSet and Statement interfaces, such as getBlob() and setBlob(), allow you to access SQL BLOB values. The Blob interface provides methods for getting the length of a SQL BLOB value, for materializing a BLOB value on the client, and for extracting a part of the BLOB.

See Also:

- Oracle C++ Call Interface Programmer's Guide for detailed information on the Blob class methods and details on instantiating and initializing a Blob object in your C++ application.

- Oracle Database Globalization Support Guide for detailed information about implementing applications in different languages.

Bfile Class

The Bfile class enables you to instantiate a Bfile object in your C++ application. You must then use methods of the Bfile class, such as the setName() method, to initialize the Bfile object which associates the object properties with an object of type BFILE in a BFILE column of the database.

See Also:

Oracle C++ Call Interface Programmer's Guide for detailed information on the Blob class methods and details on instantiating and initializing an Blob object in your C++ application.

Fixed-Width Character Set Rules

In OCCI, for fixed-width client-side character sets, the following rules apply:

- Clob: offset and amount parameters are always in characters

- Blob: offset and amount parameters are always in bytes

- Bfile: offset and amount parameters are always in bytes

Varying-Width Character Set Rules

The following rules apply only to varying-width client-side character sets:

- Offset parameter: Regardless of whether the client-side character set is varying-width, the offset parameter is always as follows:

- Clob(): in characters

- Blob(): in bytes

- Bfile(): in bytes

- Amount parameter: The amount parameter is always as follows:

- Clob: in characters, when referring to a server-side LOB

- Blob: in bytes, when referring to a client-side buffer

- Bfile: in bytes, when referring to a client-side buffer

- length(): Regardless of whether the client-side character set is varying-width, the output length is as follows:

- Clob.length(): in characters

- Blob.length(): in bytes

- Bfile.length(): in bytes

- Clob.read() and Blob.read(): With client-side character set of varying-width, CLOBs and NCLOBs:

- Input amount is in characters. Input amount refers to the number of characters to read from the server-side CLOB or NCLOB.

- Output amount is in bytes. Output amount indicates how many bytes were read into the OCCI buffer parameter, buffer.

- Clob.write() and Blob.write(): With client-side character set of varying-width, CLOBs and NCLOBs:

- Input amount is in bytes. Input amount refers to the number of bytes of data in the OCCI input buffer, buffer.

- Output amount is in characters. Output amount refers to the number of characters written into the server-side CLOB or NCLOB.

Offset and Amount Parameters for Other OCCI Operations

For all other OCCI LOB operations, irrespective of the client-side character set, the amount parameter is in characters for CLOBs and NCLOBs. These include the following:

- Clob.copy()

- Clob.erase()

- Clob.trim()

- For LoadFromFile functionality, overloaded Clob.copy()

All these operations refer to the amount of LOB data on the server.

See also:

Oracle Database Globalization Support Guide

NCLOBs in OCCI

- NCLOB instances are allowed as parameters in methods

- NCLOB instances are allowed as attributes in object types.

Amount Parameter for OCCI LOB copy() Methods

The copy() method on Clob and Blob enables you to load data from a BFILE. You can pass one of the following values for the amount parameter to this method:

- An amount smaller than the size of the BFILE to load a portion of the data

- An amount equal to the size of the BFILE to load all of the data

- The UB4MAXVAL constant to load all of the BFILE data

You cannot specify an amount larger than the length of the BFILE.

Amount Parameter for OCCI read() Operations

The read() method on an Clob, Blob, or Bfile object, reads data from a BFILE. You can pass one of the following values for the amount parameter to specify the amount of data to read:

- An amount smaller than the size of the BFILE to load a portion of the data

- An amount equal to the size of the BFILE to load all of the data

- 0 (zero) to read until the end of the BFILE in streaming mode

You cannot specify an amount larger than the length of the BFILE.

Further Information About OCCI

See Also:

- Oracle C++ Call Interface Programmer's Guide

- http://www.oracle.com/ search for articles and product information featuring OCCI.

OCCI Methods That Operate on BLOBs, BLOBs, NCLOBs, and BFILEs

OCCI methods that operate on BLOBs, CLOBs, NCLOBs, and BFILEs are as follows:

- To modify persistent LOBs, see Table 6-16

- To read or examine LOB values, see Table 6-17

- For read only methods on external LOBs (BFILEs), see Table 6-18

- Other LOB OCCI methods are described in Table 6-19

- To open and close LOBs, see Table 6-20

OCCI Methods to Modify Persistent LOB (BLOB, CLOB, and NCLOB) Values

Table 6-16 OCCI Clob and Blob Methods to Modify Persistent LOB (BLOB, CLOB, and NCLOB) Values

Function/Procedure

Description

Blob/Clob.append()

Appends CLOB or BLOB value to another LOB.

Blob/Clob.copy()

Copies all or part of a CLOB or BLOB to another LOB.

Blob/Clob.copy()

Loads BFILE data into a persistent LOB.

Blob/Clob.trim()

Truncates a CLOB or BLOB.

Blob/Clob.write()

Writes data from a buffer into a LOB, overwriting existing data.

OCCI Methods to Read or Examine Persistent LOB and BFILE Values

Table 6-17 OCCI Blob/Clob/Bfile Methods to Read or Examine persistent LOB and BFILE Values

Function/Procedure

Description

Blob/Clob.getChunkSize()

Gets the Chunk size used when reading and writing. This works on persistent LOBs and does not apply to external LOBs (BFILEs).

Blob/Clob.length()

Returns the length of a LOB or a BFILE.

Blob/Clob.read()

Reads a specified portion of a non-NULL LOB or a BFILE into a buffer.

OCCI Read-Only Methods for BFILEs

Table 6-18 OCCI Read-Only Methods for BFILES

Function/Procedure

Description

Bfile.close()

Closes an open BFILE.

Bfile.fileExists()

Checks whether a BFILE exists.

Bfile.getFileName()

Returns the name of a BFILE.

Bfile.getDirAlias()

Gets the directory object name.

Bfile.isOpen()

Checks whether a BFILE is open.

Bfile.open()

Opens a BFILE.

Other OCCI LOB Methods

Table 6-19 Other OCCI LOB Methods

Methods

Description

Clob/Blob/Bfile.operator=()

Assigns one LOB locator to another. Use = or the copy constructor.

Clob.getCharSetForm()

Returns the character set form of a LOB.

Clob.getCharSetId()

Returns the character set ID of a LOB.

Bfile.setName()

Sets the name of a BFILE.

Clob/Blob/Bfile.operator==()

Checks whether two LOB refer to the same LOB.

Clob/Blob/Bfile.isInitialized()

Checks whether a LOB is initialized.

OCCI Methods to Open and Close Internal and External LOBs

Table 6-20 OCCI Methods to Open and Close Internal and External LOBs

Function/Procedure

Description

Clob/Blob/Bfile.Open()

Opens a LOB

Clob/Blob/Bfile.isOpen()

Sees if a LOB is open

Clob/Blob/Bfile.Close()

Closes a LOB

Using C/C++ (Pro*C) to Work with LOBs

You can make changes to an entire persistent LOB, or to pieces of the beginning, middle or end of a LOB by using embedded SQL. You can access both internal and external LOBs for read purposes, and you can write to persistent LOBs.

Embedded SQL statements allow you to access data stored in BLOBs, CLOBs, NCLOBs, and BFILEs. These statements are listed in the following tables, and are discussed in greater detail later in the chapter.

See Also:

Pro*C/C++ Programmer's Guide for detailed documentation, including syntax, host variables, host variable types and example code.

First Provide an Allocated Input Locator Pointer That Represents LOB

Unlike locators in PL/SQL, locators in Pro*C/C++ are mapped to locator pointers which are then used to refer to the LOB or BFILE value.

To successfully complete an embedded SQL LOB statement you must do the following:

1. Provide an allocated input locator pointer that represents a LOB that exists in the database tablespaces or external file system before you run the statement.

2. SELECT a LOB locator into a LOB locator pointer variable

3. Use this variable in the embedded SQL LOB statement to access and manipulate the LOB value

See Also:

APIs for supported LOB operations are described in detail in:

- Chapter 12, "Operations Specific to Persistent and Temporary LOBs"

- Chapter 14, " LOB APIs for Basic Operations"

- Chapter 15, "LOB APIs for BFILE Operations"

Pro*C/C++ Statements That Operate on BLOBs, CLOBs, NCLOBs, and BFILEs

Pro*C statements that operate on BLOBs, CLOBs, and NCLOBs are listed in the following tables:

- To modify persistent LOBs, see Table 6-21

- To read or examine LOB values, see Table 6-22

- To create or free temporary LOB, or check if Temporary LOB exists, see Table 6-23

- To operate close and 'see if file exists' functions on BFILEs, see Table 6-24

- To operate on LOB locators, see Table 6-25

- For LOB buffering, see Table 6-26

- To open or close LOBs or BFILEs, see Table 6-27

Pro*C/C++ Embedded SQL Statements to Modify Persistent LOB Values

Table 6-21 Pro*C/C++: Embedded SQL Statements to Modify Persistent LOB Values

Statement

Description

APPEND

Appends a LOB value to another LOB.

COPY

Copies all or a part of a LOB into another LOB.

ERASE

Erases part of a LOB, starting at a specified offset.

LOAD FROM FILE

Loads BFILE data into a persistent LOB at a specified offset.

TRIM

Truncates a LOB.

WRITE

Writes data from a buffer into a LOB at a specified offset.

WRITE APPEND

Writes data from a buffer into a LOB at the end of the LOB.

Pro*C/C++ Embedded SQL Statements for Introspection of LOBs

Table 6-22 Pro*C/C++: Embedded SQL Statements for Introspection of LOBs

Statement

Description

DESCRIBE [CHUNKSIZE]

Gets the Chunk size used when writing. This works for persistent LOBs only. It does not apply to external LOBs (BFILEs).

DESCRIBE [LENGTH]

Returns the length of a LOB or a BFILE.

READ

reads a specified portion of a non-NULL LOB or a BFILE into a buffer.

Pro*C/C++ Embedded SQL Statements for Temporary LOBs

Table 6-23 Pro*C/C++: Embedded SQL Statements for Temporary LOBs

Statement

Description

CREATE TEMPORARY

Creates a temporary LOB.

DESCRIBE [ISTEMPORARY]

Sees if a LOB locator refers to a temporary LOB.

FREE TEMPORARY

Frees a temporary LOB.

Pro*C/C++ Embedded SQL Statements for BFILEs

Table 6-24 Pro*C/C++: Embedded SQL Statements for BFILES

Statement

Description

FILE CLOSE ALL

Closes all open BFILEs.

DESCRIBE [FILEEXISTS]

Checks whether a BFILE exists.

DESCRIBE [DIRECTORY,FILENAME]

Returns the directory object name and filename of a BFILE.

Pro*C/C++ Embedded SQL Statements for LOB Locators

Table 6-25 Pro*C/C++ Embedded SQL Statements for LOB Locators

Statement

Description

ASSIGN

Assigns one LOB locator to another.

FILE SET

Sets the directory object name and filename of a BFILE in a locator.

Pro*C/C++ Embedded SQL Statements for LOB Buffering

Table 6-26 Pro*C/C++ Embedded SQL Statements for LOB Buffering

Statement

Description

DISABLE BUFFERING

Disables the use of the buffering subsystem.

ENABLE BUFFERING

Uses the LOB buffering subsystem for subsequent reads and writes of LOB data.

FLUSH BUFFER

Flushes changes made to the LOB buffering subsystem to the database (server)

Pro*C/C++ Embedded SQL Statements to Open and Close LOBs

Table 6-27 Pro*C/C++ Embedded SQL Statements to Open and Close Persistent LOBs and External LOBs (BFILEs)

Statement

Description

OPEN

Opens a LOB or BFILE.

DESCRIBE [ISOPEN]

Sees if a LOB or BFILE is open.

CLOSE

Closes a LOB or BFILE.

Using COBOL (Pro*COBOL) to Work with LOBs

You can make changes to an entire persistent LOB, or to pieces of the beginning, middle or end of it by using embedded SQL. You can access both internal and external LOBs for read purposes, and you can also write to persistent LOBs.

Embedded SQL statements allow you to access data stored in BLOBs, CLOBs, NCLOBs, and BFILEs. These statements are listed in the following tables, and are discussed in greater detail later in the manual.

First Provide an Allocated Input Locator Pointer That Represents LOB

Unlike locators in PL/SQL, locators in Pro*COBOL are mapped to locator pointers which are then used to refer to the LOB or BFILE value. For the successful completion of an embedded SQL LOB statement you must perform the following:

1. Provide an allocated input locator pointer that represents a LOB that exists in the database tablespaces or external file system before you run the statement.

2. SELECT a LOB locator into a LOB locator pointer variable

3. Use this variable in an embedded SQL LOB statement to access and manipulate the LOB value.

See Also:

APIs for supported LOB operations are described in detail in:

- Chapter 12, "Operations Specific to Persistent and Temporary LOBs"

- Chapter 14, " LOB APIs for Basic Operations"

- Chapter 15, "LOB APIs for BFILE Operations"

Where the Pro*COBOL interface does not supply the required functionality, you can call OCI using C. Such an example is not provided here because such programs are operating system dependent.

See Also:

Pro*COBOL Programmer's Guide for detailed documentation, including syntax, host variables, host variable types, and example code.

Pro*COBOL Statements That Operate on BLOBs, CLOBs, NCLOBs, and BFILEs

The following Pro*COBOL statements operate on BLOBs, CLOBs, NCLOBs, and BFILEs:

- To modify persistent LOBs, see Table 6-28

- To read or examine internal and external LOB values, see Table 6-29

- To create or free temporary LOB, or check LOB locator, see Table 6-30

- To operate close and 'see if file exists' functions on BFILEs, see Table 6-31

- To operate on LOB locators, see Table 6-32

- For LOB buffering, see Table 6-33

- To open or close persistent LOBs or BFILEs, see Table 6-34

Pro*COBOL Embedded SQL Statements to Modify Persistent LOB Values

Table 6-28 Pro*COBOL Embedded SQL Statements to Modify LOB Values

Statement

Description

APPEND

Appends a LOB value to another LOB.

COPY

Copies all or part of a LOB into another LOB.

ERASE

Erases part of a LOB, starting at a specified offset.

LOAD FROM FILE

Loads BFILE data into a persistent LOB at a specified offset.

TRIM

Truncates a LOB.

WRITE

Writes data from a buffer into a LOB at a specified offset

WRITE APPEND

Writes data from a buffer into a LOB at the end of the LOB.

Pro*COBOL Embedded SQL Statements for Introspection of LOBs

Table 6-29 Pro*COBOL Embedded SQL Statements for Introspection of LOBs

Statement

Description

DESCRIBE [CHUNKSIZE]

Gets the Chunk size used when writing.

DESCRIBE [LENGTH]

Returns the length of a LOB or a BFILE.

READ

Reads a specified portion of a non-NULL LOB or a BFILE into a buffer.

Pro*COBOL Embedded SQL Statements for Temporary LOBs

Table 6-30 Pro*COBOL Embedded SQL Statements for Temporary LOBs

Statement

Description

CREATE TEMPORARY

Creates a temporary LOB.

DESCRIBE [ISTEMPORARY]

Sees if a LOB locator refers to a temporary LOB.

FREE TEMPORARY

Frees a temporary LOB.

Pro*COBOL Embedded SQL Statements for BFILEs

Table 6-31 Pro*COBOL Embedded SQL Statements for BFILES

Statement

Description

FILE CLOSE ALL

Closes all open BFILEs.

DESCRIBE [FILEEXISTS]

Checks whether a BFILE exists.

DESCRIBE [DIRECTORY, FILENAME]

Returns the directory object name and filename of a BFILE.

Pro*COBOL Embedded SQL Statements for LOB Locators

Table 6-32 Pro*COBOL Embedded SQL Statements for LOB Locator Statements

Statement

Description

ASSIGN

Assigns one LOB locator to another.

FILE SET

Sets the directory object name and filename of a BFILE in a locator.

Pro*COBOL Embedded SQL Statements for LOB Buffering

Table 6-33 Pro*COBOL Embedded SQL Statements for LOB Buffering

Statement

Description

DISABLE BUFFERING

Disables the use of the buffering subsystem.

ENABLE BUFFERING

Uses the LOB buffering subsystem for subsequent reads and writes of LOB data.

FLUSH BUFFER

Flushes changes made to the LOB buffering subsystem to the database (server)

Pro*COBOL Embedded SQL Statements for Opening and Closing LOBs and BFILEs

Table 6-34 Pro*COBOL Embedded SQL Statements for Opening and CLosing Persistent LOBs and BFILEs

Statement

Description

OPEN

Opens a LOB or BFILE.

DESCRIBE [ISOPEN]

Sees if a LOB or BFILE is open.

CLOSE

Closes a LOB or BFILE.

Using Visual Basic (Oracle Objects for OLE) to Work with LOBs

Oracle Objects for OLE (OO4O) is a set of programmable COM objects that simplifies the development of applications designed to communicate with an Oracle Database. OO4O offers high performance database access. It also provides easy access to features unique to Oracle, yet otherwise cumbersome or inefficient to use from other ODBC or OLE DB-based components, such as ADO.

You can make changes to an entire persistent LOB, or to pieces of the beginning, middle or end of it, with the Oracle Objects for OLE (OO4O) API, by using one of the following objects interfaces:

- OraBlob: To provide methods for performing operations on BLOB datatypes in the database

- OraClob: To provide methods for performing operations on CLOB datatypes in the database

- OraBFile: To provide methods for performing operations on BFILE data stored in operating system files.

Note:

OracleBlob and OracleClob have been deprecated and no longer work

OO4O Syntax Reference

The OO4O syntax reference and further information is viewed from the OO4O online help. Oracle Objects for OLE (OO4O), a Windows-based product included with the database, has no manuals, only online help.

Its online help is available through the Application Development submenu of the database installation. To view specific methods and properties from the Help Topics menu, select the Contents tab > OO4O Automation Server > Methods or Properties.

For further information about OO4O, refer to the following Web site:

- http://www.oracle.com/technology/index.html

Select Products > Internet Tools > Programmer. Scroll down to "Oracle Objects for OLE". At the bottom of the page is a list of useful articles for using the interfaces.

- http://www.oracle.com/ Search for articles on OO4O or Oracle Objects for OLE.

OraBlob, OraClob, and OraBfile Object Interfaces Encapsulate Locators

These interfaces encapsulate LOB locators, so you do not deal directly with locators, but instead, can use methods and properties provided to perform operations and get state information.

OraBlob and OraClob Objects Are Retrieved as Part of Dynaset

When OraBlob and OraClob objects are retrieved as a part of a dynaset, these objects represent LOB locators of the dynaset current row. If the dynaset current row changes due to a move operation, then the OraBlob and OraClob objects represent the LOB locator for the new current row.

Use the Clone Method to Retain Locator Independent of the Dynaset Move

To retain the LOB locator of the OraBlob and OraClob object independent of the dynaset move operation, use the Clone method. This method returns the OraBlob and OraClob object. You can also use these objects as PL/SQL bind parameters.

Example of OraBlob and OraBfile

The following example shows usage of OraBlob and OraBfile.

Dim OraDyn as OraDynaset, OraSound1 as OraBLOB, OraSoundClone as OraBlob, OraMyBfile as OraBFile

OraConnection.BeginTrans
set OraDyn = OraDb.CreateDynaset("select * from print_media order by product_id", ORADYN_DEFAULT)
set OraSound1 = OraDyn.Fields("Sound").value
set OraSoundClone = OraSound1

OraParameters.Add "id", 1,ORAPARAM_INPUT
OraParameters.Add "mybfile", Empty,ORAPARAM_OUTPUT
OraParameters("mybfile").ServerType = ORATYPE_BFILE

OraDatabase.ExecuteSQL ("begin  GetBFile(:id, :mybfile ") end")

Set OraMyBFile = OraParameters("mybfile").value
'Go to Next row
OraDyn.MoveNext

OraDyn.Edit
'Lets update OraSound1 data with that from the BFILE
OraSound1.CopyFromBFile  OraMyBFile
OraDyn.Update

OraDyn.MoveNext
'Go to Next row
OraDyn.Edit
'Lets update OraSound1 by appending with LOB data from 1st row represenetd by
'OraSoundClone
OraSound1.Append  OraSoundClone
OraDyn.Update

OraConnection.CommitTrans

In the preceding example:

OraSound1 — represents the locator for the current row in the dynaset OraSoundClone — represents the locator for the 1st row.

A change in the current row (say a OraDyn.MoveNext) means the following:

OraSound1 — will represent the locator for the 2nd row.

OraSoundClone — will represent the locator in the 1st row. OraSoundClone only refers the locator for the 1st row irrespective of any OraDyn row navigation).

OraMyBFile — refers to the locator obtained from an PL/SQL "OUT" parameter as a result of executing a PL/SQL procedure, either by doing an OraDatabase.ExecuteSQL.

Note:

A LOB obtained by executing SQL is only valid for the duration of the transaction. For this reason, "BEGINTRANS" and "COMMITTRANS" are used to specify the duration of the transaction.

OO4O Methods and Properties to Access Data Stored in LOBs

Oracle Objects for OLE (OO4O) includes methods and properties that you can use to access data stored in BLOBs, CLOBs, NCLOBs, and BFILEs.

See Also:

APIs for supported LOB operations are described in detail in:

- Chapter 12, "Operations Specific to Persistent and Temporary LOBs"

- Chapter 14, " LOB APIs for Basic Operations"

- Chapter 15, "LOB APIs for BFILE Operations"

See Also:

The OO4O online help for detailed information including parameters, parameter types, return values, and example code. Oracle Objects for OLE (OO4O), a Windows-based product included with the database, has no manuals, only online help. The OO4O online help is available through the Application Development submenu of the database installation.

The following OO4O methods and properties operate on BLOBs, CLOBs, NCLOBs, and BFILEs:

- To modify persistent LOBs, see Table 6-35

- To read or examine internal and external LOB values, see Table 6-36

- To open and close BFILEs, see Table 6-37

- For LOB buffering, see Table 6-38

- Properties such as to see if LOB is NULL, or to get or set polling amount, see Table 6-39

- For read-only BFILE methods, see Table 6-40

- For BFILE properties, see Table 6-41

OO4O Methods to Modify BLOB, CLOB, and NCLOB Values

Table 6-35 OO4O Methods to Modify BLOB, CLOB, and NCLOB Values

Methods

Description

OraBlob.Append
OraClob.Append

Appends BLOB value to another LOB.
Appends CLOB or NCLOB value to another LOB.

OraBlob.Copy
OraClob.Copy

Copies a portion of a BLOB into another LOB
Copies a portion of a CLOB or NCLOB into another LOB

OraBlob.Erase
OraClob.Erase

Erases part of a BLOB, starting at a specified offset
Erases part of a CLOB or NCLOB, starting at a specified offset

OraBlob.CopyFromBFile
OraClob.CopyFromBFile

Loads BFILE data into an internal BLOB
Loads BFILE data into an internal CLOB or NCLOB

OraBlob.Trim
OraClob.Trim

Truncates a BLOB
Truncates a CLOB or NCLOB

OraBlob.CopyFromFile
OraClob.CopyFromFile

Writes data from a file to a BLOB
Writes data from a file to a CLOB or NCLOB

OraBlob.Write
OraClob.Write

Writes data to the BLOB
Writes data to the CLOB or NCLOB

OO4O Methods to Read or Examine Internal and External LOB Values

Table 6-36 OO4O Methods to Read or Examine Internal and External LOB Values

Function/Procedure

Description

OraBlob.Read
OraClob.Read

OraBFile.Read

Reads a specified portion of a non-NULL BLOB into a buffer
Reads a specified portion of a non-NULL CLOB into a buffer

Reads a specified portion of a non-NULL BFILE into a buffer

OraBlob.CopyToFile
OraClob.CopyToFile

Reads a specified portion of a non-NULL BLOB to a file
Reads a specified portion of a non-NULL CLOB to a file

OO4O Methods to Open and Close External LOBs (BFILEs)

Table 6-37 OO4O Methods to Open and Close External LOBs (BFILEs)

Method

Description

OraBFile.Open

Opens BFILE.

OraBFile.Close

Closes BFILE.

OO4O Methods for Persistent LOBBuffering

Table 6-38 OO4O Methods for Persistent LOB Buffering

Method

Description

OraBlob.FlushBuffer
OraClob.FlushBuffer

Flushes changes made to the BLOB buffering subsystem to the database
Flushes changes made to the CLOB buffering subsystem to the database

OraBlob.EnableBuffering
OraClob.EnableBuffering

Enables buffering of BLOB operations
Enables buffering of CLOB operations

OraBlob.DisableBuffering
OraClob.DisableBuffering

Disables buffering of BLOB operations
Disables buffering of CLOB operations

OO4O Properties for Operating on LOBs

Table 6-39 OO4O Properties for Operating on LOBs

Property

Description

IsNull (Read)

Indicates when a LOB is NULL

PollingAmount(Read/Write)

Gets/Sets total amount for Read/Write polling operation

Offset(Read/Write)

Gets/Sets offset for Read/Write operation. By default, it is set to 1.

Status(Read)

Returns the polling status.Possible values are

- ORALOB_NEED_DATA There is more data to be read or written

- ORALOB_NO_DATA There is no more data to be read or written

- ORALOB_SUCCESS_LOB data read/written successfully

Size(Read)

Returns the length of the LOB data

OO4O Read-Only Methods for External Lobs (BFILEs)

Table 6-40 OO4O Read-Only Methods for External LOBs (BFILEs)

Methods

Description

OraBFile.Close

Closes an open BFILE

OraBFile.CloseAll

Closes all open BFILEs

OraBFile.Open

Opens a BFILE

OraBFile.IsOpen

Determines if a BFILE is open

OO4O Properties for Operating on External LOBs (BFILEs)

Table 6-41 OO4O Properties for Operating on External LOBs (BFILEs)

Property

Description

OraBFile.DirectoryName

Gets/Sets the server side directory object name.

OraBFile.FileName(Read/Write)

Gets/Sets the server side filename.

OraBFile.Exists

Checks whether a BFILE exists.

Using Java (JDBC) to Work with LOBs

You can perform the following tasks on LOBs with Java (JDBC):

- Modifying Internal Persistent LOBs Using Java

- Reading Internal Persistent LOBs and External LOBs (BFILEs) with Java

- Calling DBMS_LOB Package from Java (JDBC)

- Referencing LOBs Using Java (JDBC)

- Create and Manipulate Temporary LOBs and Store Them in Tables as Permanent LOBs. See JDBC Temporary LOB APIs

Modifying Internal Persistent LOBs Using Java

You can make changes to an entire persistent LOB, or to pieces of the beginning, middle, or end of a persistent LOB in Java by means of the JDBC API using the classes:

- oracle.sql.BLOB

- oracle.sql.CLOB

These classes implement java.sql.Blob and java.sql.Clob interfaces according to the JDBC 3.0 specification, which has methods for LOB modification. They also include legacy Oracle proprietary methods for LOB modification. These legacy methods are marked as deprecated and may be removed in a future release.

If you use JDK 1.4 or higher, then you can use variables typed java.sql.Blob and java.sql.Clob.

The JDBC 3.0 methods are included in classes12.jar, so that they can be used in JDK 1.2 or 1.3, but since they are not part of the java.sql.Blob and java.sql.Clob interfaces in those JDK versions, you must use variables typed or cast to oracle.sql.BLOB or oracle.sql.CLOB.

Table 6-42 and Table 6-43 show the conversions between Oracle proprietary methods that have been deprecated and JDBC 3.0 standard methods.

Table 6-42 BLOB Method Equivalents

Oracle Proprietary Method (Deprecated)

JDBC 3.0 Standard Method Replacement

putBytes(long pos, byte [] bytes)

setBytes(long pos, byte[] bytes)

putBytes(long pos, byte [] bytes, int length)

setBytes(long pos, byte[] bytes, int offset, int len)

getBinaryOutputStream(long pos)

setBinaryStream(long pos)

trim (long len)

truncate(long len)

Table 6-43 CLOB Method Equivalents

Oracle Proprietary Method (Deprecated)

JDBC 3.0 Standard Method Replacement

putString(long pos, String str)

setString(long pos, String str)

N/A

setString(long pos, String str, int offset, int len)

getAsciiOutputStream(long pos)

setAsciiStream(long pos)

getCharacterOutputStream(long pos)

setCharacterStream(long pos)

trim (long len)

truncate(long len)

Reading Internal Persistent LOBs and External LOBs (BFILEs) with Java

With JDBC you can use Java to read both internal persistent LOBs and external LOBs (BFILEs).

BLOB, CLOB, and BFILE Classes

- BLOB and CLOB Classes. In JDBC theses classes provide methods for performing operations on large objects in the database including BLOB and CLOB data types.

- BFILE Class. In JDBC this class provides methods for performing operations on BFILE data in the database.

The BLOB, CLOB, and BFILE classes encapsulate LOB locators, so you do not deal with locators but instead use methods and properties provided to perform operations and get state information.

Calling DBMS_LOB Package from Java (JDBC)

Any LOB functionality not provided by these classes can be accessed by a call to the PL/SQL DBMS_LOB package. This technique is used repeatedly in the examples throughout this manual.

Referencing LOBs Using Java (JDBC)

You can get a reference to any of the preceding LOBs in the following two ways:

- As a column of an OracleResultSet

- As an OUT type PL/SQL parameter from an OraclePreparedStatement

Using OracleResultSet: BLOB and CLOB Objects Retrieved

When BLOB and CLOB objects are retrieved as a part of an OracleResultSet, these objects represent LOB locators of the currently selected row.

If the current row changes due to a move operation, for example, rset.next(), then the retrieved locator still refers to the original LOB row.

To retrieve the locator for the most current row, you must call getBLOB(), getCLOB(), or getBFILE() on the OracleResultSet each time a move operation is made depending on whether the instance is a BLOB, CLOB or BFILE.

JDBC Syntax References and Further Information

For further JDBC syntax and information about using JDBC with LOBs:

See Also:

- Oracle Database JDBC Developer's Guide and Reference, "Working with LOBs and BFILEs" chapter, for detailed documentation, including parameters, parameter types, return values, and example code.

- http://www.oracle.com/technology/index.html

JDBC Methods for Operating on LOBs

The following JDBC methods operate on BLOBs, CLOBs, and BFILEs:

- BLOBs:

- To modify BLOB values, see Table 6-44

- To read or examine BLOB values, see Table 6-45

- For BLOB buffering, see Table 6-46

- Temporary BLOBs: Creating, checking if LOB is open, and freeing. See Table 6-54

- Opening, closing, and checking if BLOB is open, see Table 6-54

- Truncating BLOBs, see Table 6-57

- BLOB streaming API, see Table 6-59

- CLOBs:

- To read or examine CLOB values, see Table 6-48

- For CLOB buffering, see Table 6-49

- To modify CLOBs, see Table 6-59

- Temporary CLOBs:

- Opening, closing, and checking if CLOB is open, see Table 6-55

- Truncating CLOBs, see Table 6-58

- CLOB streaming API, see Table 6-60

- BFILEs:

- To read or examine BFILEs, see Table 6-50

- For BFILE buffering, see Table 6-51

- Opening, closing, and checking if BFILE is open, see Table 6-56

- BFILE streaming API, see Table 6-61

JDBC oracle.sql.BLOB Methods to Modify BLOB Values

Table 6-44 JDBC oracle.sql.BLOB Methods To Modify BLOB Values

Method

Description

int setBytes(long, byte[])

Inserts the byte array into the BLOB, starting at the given offset

JDBC oracle.sql.BLOB Methods to Read or Examine BLOB Values

Table 6-45 JDBC oracle.sql.BLOB Methods to Read or Examine BLOB Values

Method

Description

byte[] getBytes(long, int)

Gets the contents of the LOB as an array of bytes, given an offset

long position(byte[],long)

Finds the given byte array within the LOB, given an offset

long position(Blob,long)

Finds the given BLOB within the LOB

public boolean equals(java.lang.Object)

Compares this LOB with another. Compares the LOB locators.

public long length()

Returns the length of the LOB

public int getChunkSize()

Returns the ChunkSize of the LOB

JDBC oracle.sql.BLOB Methods and Properties for BLOB Buffering

Table 6-46 JDBC oracle.sql.BLOB Methods and Properties for BLOB Buffering

Method

Description

public java.io.InputStream getBinaryStream())

Streams the LOB as a binary stream

public java.io.OutputStream setBinaryStream()

Retrieves a stream that can be used to write to the BLOB value that this Blob object represents

JDBC oracle.sql.CLOB Methods to Modify CLOB Values

Table 6-47 JDBC oracle.sql.CLOB Methods to Modify CLOB Values

Method

Description

int setString(long, java.lang.String)

JDBC 3.0: Writes the given Java String to the CLOB value that this Clob object designates at the position pos.

int putChars(long, char[])

Inserts the character array into the LOB, starting at the given offset

JDBC oracle.sql.CLOB Methods to Read or Examine CLOB Value

Table 6-48 JDBC oracle.sql.CLOB Methods to Read or Examine CLOB Values

Method

Description

java.lang.String getSubString(long, int)

Returns a substring of the LOB as a string

int getChars(long, int, char[])

Reads a subset of the LOB into a character array

long position(java.lang.String, long)

Finds the given String within the LOB, given an offset

long position(oracle.jdbc2.Clob, long)

Finds the given CLOB within the LOB, given an offset

long length()

Returns the length of the LOB

int getChunkSize()

Returns the ChunkSize of the LOB

JDBC oracle.sql.CLOB Methods and Properties for CLOB Buffering

Table 6-49 JDBC oracle.sql.CLOB Methods and Properties for CLOB Buffering

Method

Description

java.io.InputStream getAsciiStream()

Implements the Clob interface method. Gets the CLOB value designated by this Clob object as a stream of ASCII bytes

java.io.OutputStream setAsciiStream(long pos)

JDBC 3.0: Retrieves a stream to be used to write ASCII characters to the CLOB value that this Clob object represents, starting at position pos

java.io.Reader getCharacterStream()

Reads the CLOB as a character stream

java.io.Writer setCharacterStream(long pos)

JDBC 3.0: Retrieves a stream to be used to write Unicode characters to the CLOB value that this Clob object represents, starting at position pos

JDBC oracle.sql.BFILE Methods to Read or Examine External LOB (BFILE) Values

Table 6-50 JDBC oracle.sql.BFILE Methods to Read or Examine External LOB (BFILE) Values

Method

Description

byte[] getBytes(long, int)

Gets the contents of the BFILE as an array of bytes, given an offset

int getBytes(long, int, byte[])

Reads a subset of the BFILE into a byte array

long position(oracle.sql.BFILE, long)

Finds the first appearance of the given BFILE contents within the LOB, from the given offset

long position(byte[], long)

Finds the first appearance of the given byte array within the BFILE, from the given offset

long length()

Returns the length of the BFILE

boolean fileExists()

Checks if the operating system file referenced by this BFILE exists

public void openFile()

Opens the operating system file referenced by this BFILE

public void closeFile()

Closes the operating system file referenced by this BFILE

public boolean isFileOpen()

Checks if this BFILE is already open

public java.lang.String getDirAlias()

Gets the directory object name for this BFILE

public java.lang.String getName()

Gets the file name referenced by this BFILE

JDBC oracle.sql.BFILE Methods and Properties for BFILE Buffering

Table 6-51 JDBC oracle.sql.BFILE Methods and Properties for BFILE Buffering

Method

Description

public java.io.InputStream getBinaryStream()

Reads the BFILE as a binary stream

JDBC Temporary LOB APIs

Oracle Database JDBC drivers contain APIs to create and close temporary LOBs. These APIs can replace workarounds that use the following procedures from the DBMS_LOB PL/SQL package in prior releases:

- DBMS_LOB.createTemporary()

- DBMS_LOB.isTemporary()

- DBMS_LOB.freeTemporary()

Table 6-52 JDBC: Temporary BLOB APIs

Methods

Description

public static BLOB createTemporary(Connection conn,
boolean cache, int duration) throws SQLException

Creates a temporary BLOB

public static boolean isTemporary(BLOB blob)
throws SQLException

Checks if the specified BLOB locator refers to a temporary BLOB

public boolean isTemporary() throws SQLException

Checks if the current BLOB locator refers to a temporary BLOB

public static void freeTemporary(BLOB temp_blob)
throws SQLException

Frees the specified temporary BLOB

public void freeTemporary() throws SQLException

Frees the temporary BLOB

Table 6-53 JDBC: Temporary CLOB APIs

Methods

Description

public static CLOB createTemporary(Connection conn,
boolean cache, int duration) throws SQLException

Creates a temporary CLOB

public static boolean isTemporary(CLOB clob)
throws SQLException

Checks if the specified CLOB locator refers to a temporary CLOB

public boolean isTemporary() throws SQLException

Checks if the current CLOB locator refers to a temporary CLOB

public static void freeTemporary(CLOB temp_clob)
throws SQLException

Frees the specified temporary CLOB

public void freeTemporary() throws SQLException

Frees the temporary CLOB

JDBC: Opening and Closing LOBs

oracle.sql.CLOB class is the Oracle JDBC driver implementation of standard JDBC java.sql.Clob interface. Table 6-53 lists the Oracle extension APIs in oracle.sql.CLOB for accessing temporary CLOBs.

Oracle Database JDBC drivers contain APIs to explicitly open and close LOBs. These APIs replace previous techniques that use DBMS_LOB.open() and DBMS_LOB.close().

JDBC: Opening and Closing BLOBs

oracle.sql.BLOB class is the Oracle JDBC driver implementation of standard JDBC java.sql.Blob interface. Table 6-54 lists the Oracle extension APIs in oracle.sql.BLOB that open and close BLOBs.

Table 6-54 JDBC: Opening and Closing BLOBs

Methods

Description

public void open(int mode) throws SQLException

Opens the BLOB

public boolean isOpen() throws SQLException

Sees if the BLOB is open

public void close() throws SQLException

Closes the BLOB

Opening the BLOB Using JDBC

To open a BLOB, your JDBC application can use the open method as defined in oracle.sql.BLOB class as follows:

/**
* Open a BLOB in the indicated mode. Valid modes include MODE_READONLY,
* and MODE_READWRITE. It is an error to open the same LOB twice.
*/
public void open (int mode) throws SQLException

Possible values of the mode parameter are:

public static final int MODE_READONLY
public static final int MODE_READWRITE

Each call to open opens the BLOB. For example:

BLOB blob = ...
blob.open (BLOB.MODE_READWRITE);

Checking If the BLOB Is Open Using JDBC

To see if a BLOB is opened, your JDBC application can use the isOpen method defined in oracle.sql.BLOB. The return Boolean value indicates whether the BLOB has been previously opened or not. The isOpen method is defined as follows:

/**
* Check whether the BLOB is opened.
* @return true if the LOB is opened.
*/
public boolean isOpen () throws SQLException

The usage example is:

BLOB blob = ...
// See if the BLOB is opened
boolean isOpen = blob.isOpen ();

Closing the BLOB Using JDBC

To close a BLOB, your JDBC application can use the close method defined in oracle.sql.BLOB. The close API is defined as follows:

/**
* Close a previously opened BLOB.
*/
public void close () throws SQLException

The usage example is:

BLOB blob = ...
// close the BLOB
blob.close ();

JDBC: Opening and Closing CLOBs

Class oracle.sql.CLOB is the Oracle JDBC driver implementation of the standard JDBC java.sql.Clob interface. Table 6-55 lists the Oracle extension APIs in oracle.sql.CLOB to open and close CLOBs.

Table 6-55 JDBC: Opening and Closing CLOBs

Methods

Description

public void open(int mode) throws SQLException

Open the CLOB

public boolean isOpen() throws SQLExceptio

See if the CLOB is opened

public void close() throws SQLException

Close the CLOB

Opening the CLOB Using JDBC

To open a CLOB, your JDBC application can use the open method defined in oracle.sql.CLOB class as follows:

/**
* Open a CLOB in the indicated mode. Valid modes include MODE_READONLY,
* and MODE_READWRITE. It is an error to open the same LOB twice.
*/
public void open (int mode) throws SQLException

The possible values of the mode parameter are:

public static final int MODE_READONLY
public static final int MODE_READWRITE

Each call to open opens the CLOB. For example,

CLOB clob = ...
clob.open (CLOB.MODE_READWRITE);

Checking If the CLOB Is Open Using JDBC

To see if a CLOB is opened, your JDBC application can use the isOpen method defined in oracle.sql.CLOB. The return Boolean value indicates whether the CLOB has been previously opened or not. The isOpen method is defined as follows:

/**
* Check whether the CLOB is opened.
* @return true if the LOB is opened.
*/
public boolean isOpen () throws SQLException

The usage example is:

CLOB clob = ...
// See if the CLOB is opened
boolean isOpen = clob.isOpen ();

Closing the CLOB Using JDBC

To close a CLOB, the JDBC application can use the close method defined in oracle.sql.CLOB. The close API is defined as follows:

/**
* Close a previously opened CLOB.
*/
public void close () throws SQLException

The usage example is:

CLOB clob = ...
// close the CLOB
clob.close ();

JDBC: Opening and Closing BFILEs

oracle.sql.BFILE class wraps the database BFILE object. Table 6-56 lists the Oracle extension APIs in oracle.sql.BFILE for opening and closing BFILEs.

Table 6-56 JDBC API Extensions for Opening and Closing BFILEs

Methods

Description

public void open() throws SQLException

Opens the BFILE

public void open(int mode) throws SQLException

Opens the BFILE

public boolean isOpen() throws SQLException

Checks if the BFILE is open

public void close() throws SQLException

Closes the BFILE

Opening BFILEs

To open a BFILE, your JDBC application can use the OPEN method defined in oracle.sql.BFILE class as follows:

/**
* Open a external LOB in the readonly mode. It is an error
* to open the same LOB twice.
*/
public void open () throws SQLException

/**
* Open a external LOB in the indicated mode. Valid modes include
* MODE_READONLY only. It is an error to open the same
* LOB twice.
*/
public void open (int mode) throws SQLException

The only possible value of the mode parameter is:

public static final int MODE_READONLY

Each call to open opens the BFILE. For example,

BFILE bfile = ...
bfile.open ();

Checking If the BFILE Is Open

To see if a BFILE is opened, your JDBC application can use the isOpen method defined in oracle.sql.BFILE. The return Boolean value indicates whether the BFILE has been previously opened or not. The isOpen method is defined as follows:

/**
* Check whether the BFILE is opened.
* @return true if the LOB is opened.
*/
public boolean isOpen () throws SQLException

The usage example is:

BFILE bfile = ...
// See if the BFILE is opened
boolean isOpen = bfile.isOpen ();

Closing the BFILE

To close a BFILE, your JDBC application can use the close method defined in oracle.sql.BFILE. The close API is defined as follows:

/**
* Close a previously opened BFILE.
*/
public void close () throws SQLException

The usage example is --

BFILE bfile = ...
// close the BFILE
bfile.close ();

Usage Example (OpenCloseLob.java)

/*
* This sample shows how to open/close BLOB and CLOB.
*/

// You need to import the java.sql package to use JDBC
import java.sql.*;

// You need to import the oracle.sql package to use oracle.sql.BLOB
import oracle.sql.*;

class OpenCloseLob
{
public static void main (String args [])
throws SQLException
{
// Load the Oracle JDBC driver
DriverManager.registerDriver(new oracle.jdbc.driver.OracleDriver());

String url = "jdbc:oracle:oci8:@";
try {
String url1 = System.getProperty("JDBC_URL");
if (url1 != null)
url = url1;
} catch (Exception e) {
// If there is any security exception, ignore it
// and use the default
}

// Connect to the database
Connection conn =
DriverManager.getConnection (url, "scott", "tiger");
// It is faster when auto commit is off
conn.setAutoCommit (false);

// Create a Statement
Statement stmt = conn.createStatement ();

try
{
stmt.execute ("drop table basic_lob_table");
}
catch (SQLException e)
{
// An exception could be raised here if the table did not exist already.
}

// Create a table containing a BLOB and a CLOB
stmt.execute ("create table basic_lob_table (x varchar2 (30), b blob, c clob)");

// Populate the table
stmt.execute (
"insert into basic_lob_table values"
+ " ('one', '010101010101010101010101010101', 'onetwothreefour')");

// Select the lobs
ResultSet rset = stmt.executeQuery ("select * from basic_lob_table");
while (rset.next ())
{
// Get the lobs
BLOB blob = (BLOB) rset.getObject (2);
CLOB clob = (CLOB) rset.getObject (3);

// Open the lobs
System.out.println ("Open the lobs");
blob.open (BLOB.MODE_READWRITE);
clob.open (CLOB.MODE_READWRITE);

// Check if the lobs are opened
System.out.println ("blob.isOpen()="+blob.isOpen());
System.out.println ("clob.isOpen()="+clob.isOpen());

// Close the lobs
System.out.println ("Close the lobs");
blob.close ();
clob.close ();

// Check if the lobs are opened
System.out.println ("blob.isOpen()="+blob.isOpen());
System.out.println ("clob.isOpen()="+clob.isOpen());
}

// Close the ResultSet
rset.close ();

// Close the Statement
stmt.close ();

// Close the connection
conn.close ();
}
}

Truncating LOBs Using JDBC

Oracle Database JDBC drivers contain APIs to truncate persistent LOBs. These APIs replace previous techniques that used DBMS_LOB.trim().

JDBC: Truncating BLOBs

oracle.sql.BLOB class is Oracle JDBC driver implementation of the standard JDBC java.sql.Blob interface. Table 6-57 lists the Oracle extension API in oracle.sql.BLOB that truncates BLOBs.

Table 6-57 JDBC: Truncating BLOBs

Methods

Description

public void truncate(long newlen) throws SQLException

Truncates the BLOB

The truncate API is defined as follows:

/**
*Truncate the value of the BLOB to the length you specify in the newlen parameter.
* @param newlen the new length of the BLOB.
*/
public void truncate (long newlen) throws SQLException

The newlen parameter specifies the new length of the BLOB.

JDBC: Truncating CLOBs

oracle.sql.CLOB class is the Oracle JDBC driver implementation of standard JDBC java.sql.Clob interface. Table 6-58 lists the Oracle extension API in oracle.sql.CLOB that truncates CLOBs.

Table 6-58 JDBC: Truncating CLOBs

Methods

Description

public void truncate(long newlen) throws SQLException

Truncates the CLOB

The truncate API is defined as follows:

/**
*Truncate the value of the CLOB to the length you specify in the newlen parameter.
* @param newlen the new length of the CLOB.
*/
public void truncate (long newlen) throws SQLException

The newlen parameter specifies the new length of the CLOB.

See:

"Trimming LOB Data", for an example.

JDBC BLOB Streaming APIs

The JDBC interface provided with the database includes LOB streaming APIs that enable you to read from or write to a LOB at the requested position from a Java stream.

The oracle.sql.BLOB class implements the standard JDBC java.sql.Blob interface. Table 6-59 lists BLOB Streaming APIs.

Table 6-59 JDBC: BLOB Streaming APIs

Methods

Description

public java.io.OutputStream
setBinaryStream (long pos) throws SQLException

JDBC 3.0: Retrieves a stream that can be used to write to the BLOB value that this Blob object represents, starting at position pos

public java.io.InputStream
getBinaryStream() throws SQLException

JDBC 3.0: Retrieves a stream that can be used to read the BLOB value that this Blob object represents, starting at the beginning

public java.io.InputStream
getBinaryStream(long pos) throws SQLException

Oracle extension: Retrieves a stream that can be used to read the BLOB value that this Blob object represents, starting at position pos

These APIs are defined as follows:

/**
* Write to the BLOB from a stream at the requested position.
*
* @param pos is the position data to be put.
* @return a output stream to write data to the BLOB
*/
public java.io.OutputStream setBinaryStream(long pos) throws SQLException

/**
* Read from the BLOB as a stream at the requested position.
*
* @param pos is the position data to be read.
* @return a output stream to write data to the BLOB
*/
public java.io.InputStream getBinaryStream(long pos) throws SQLException

JDBC CLOB Streaming APIs

The oracle.sql.CLOB class is the Oracle JDBC driver implementation of standard JDBC java.sql.Clob interface. Table 6-60 lists the CLOB streaming APIs.

Table 6-60 JDBC: CLOB Streaming APIs

Methods

Description

public java.io.OutputStream
setAsciiStream (long pos) throws SQLException

JDBC 3.0: Retrieves a stream to be used to write ASCII characters to the CLOB value that this Clob object represents, starting at position pos

public java.io.Writer
setCharacterStream (long pos) throws SQLException

JDBC 3.0: Retrieves a stream to be used to write Unicode characters to the CLOB value that this Clob object represents, starting, at position pos

public java.io.InputStream
getAsciiStream() throws SQLException

JDBC 3.0: Retrieves a stream that can be used to read ASCII characters from the CLOB value that this Clob object represents, starting at the beginning

public java.io.InputStream
getAsciiStream(long pos) throws SQLException

Oracle extension: Retrieves a stream that can be used to read ASCII characters from the CLOB value that this Clob object represents, starting at position pos

public java.io.Reader
getCharacterStream() throws SQLException

JDBC 3.0: Retrieves a stream that can be used to read Unicode characters from the CLOB value that this Clob object represents, starting at the beginning

public java.io.Reader
getCharacterStream(long pos) throws SQLException

Oracle extension: Retrieves a stream that can be used to read Unicode characters from the CLOB value that this Clob object represents, starting at position pos

These APIs are defined as follows:

/**
* Write to the CLOB from a stream at the requested position.
* @param pos is the position data to be put.
* @return a output stream to write data to the CLOB
*/
public java.io.OutputStream setAsciiStream(long pos) throws SQLException

/**

* Write to the CLOB from a stream at the requested position.
* @param pos is the position data to be put.
* @return a output stream to write data to the CLOB
*/
public java.io.Writer setCharacterStream(long pos) throws SQLException

/**
* Read from the CLOB as a stream at the requested position.
* @param pos is the position data to be put.
* @return a output stream to write data to the CLOB
*/
public java.io.InputStream getAsciiStream(long pos) throws SQLException

/**
* Read from the CLOB as a stream at the requested position.
* @param pos is the position data to be put.
* @return a output stream to write data to the CLOB
*/
public java.io.Reader getCharacterStream(long pos) throws SQLException

BFILE Streaming APIs

oracle.sql.BFILE class wraps the database BFILEs. Table 6-61 lists the Oracle extension APIs in oracle.sql.BFILE that reads BFILE content from the requested position.

Table 6-61 JDBC: BFILE Streaming APIs

Methods

Description

public java.io.InputStream
getBinaryStream(long pos) throws SQLException

Reads from the BFILE as a stream

These APIs are defined as follows:

/**
* Read from the BLOB as a stream at the requested position.
*
* @param pos is the position data to be read.
* @return a output stream to write data to the BLOB
*/
public java.io.InputStream getBinaryStream(long pos) throws SQLException

JDBC BFILE Streaming Example (NewStreamLob.java)

/*
* This sample shows how to read/write BLOB and CLOB as streams.
*/

import java.io.*;

// You need to import the java.sql package to use JDBC
import java.sql.*;

// You need to import the oracle.sql package to use oracle.sql.BLOB
import oracle.sql.*;

class NewStreamLob
{
public static void main (String args [])  throws Exception
{
// Load the Oracle JDBC driver
DriverManager.registerDriver(new oracle.jdbc.driver.OracleDriver());

String url = "jdbc:oracle:oci8:@";
try {
String url1 = System.getProperty("JDBC_URL");
if (url1 != null)
url = url1;
} catch (Exception e) {
// If there is any security exception, ignore it
// and use the default
}

// Connect to the database
Connection conn =
DriverManager.getConnection (url, "scott", "tiger");
// It is faster when auto commit is off
conn.setAutoCommit (false);

// Create a Statement
Statement stmt = conn.createStatement ();

try
{
stmt.execute ("drop table basic_lob_table");
}
catch (SQLException e)
{
// An exception could be raised here if the table did not exist already.
}

// Create a table containing a BLOB and a CLOB
stmt.execute (
"create table basic_lob_table"
+ "(x varchar2 (30), b blob, c clob)");

// Populate the table
stmt.execute (
"insert into basic_lob_table values"
+ "('one', '010101010101010101010101010101', 'onetwothreefour')");

System.out.println ("Dumping lobs");

// Select the lobs
ResultSet rset = stmt.executeQuery ("select * from basic_lob_table");
while (rset.next ())
{
// Get the lobs
BLOB blob = (BLOB) rset.getObject (2);
CLOB clob = (CLOB) rset.getObject (3);

// Print the lob contents
dumpBlob (conn, blob, 1);
dumpClob (conn, clob, 1);

// Change the lob contents
fillClob (conn, clob, 11, 50);
fillBlob (conn, blob, 11, 50);
}
rset.close ();

System.out.println ("Dumping lobs again");

rset = stmt.executeQuery ("select * from basic_lob_table");
while (rset.next ())
{
// Get the lobs
BLOB blob = (BLOB) rset.getObject (2);
CLOB clob = (CLOB) rset.getObject (3);

// Print the lobs contents
dumpBlob (conn, blob, 11);
dumpClob (conn, clob, 11);
}
// Close all resources
rset.close();
stmt.close();
conn.close();
}

// Utility function to dump Clob contents
static void dumpClob (Connection conn, CLOB clob, long offset)
throws Exception
{
// get character stream to retrieve clob data
Reader instream = clob.getCharacterStream(offset);

// create temporary buffer for read
char[] buffer = new char[10];

// length of characters read
int length = 0;

// fetch data
while ((length = instream.read(buffer)) != -1)
{
System.out.print("Read " + length + " chars: ");

for (int i=0; i<length; i++)
System.out.print(buffer[i]);
System.out.println();
}

// Close input stream
instream.close();
}

// Utility function to dump Blob contents
static void dumpBlob (Connection conn, BLOB blob, long offset)
throws Exception
{
// Get binary output stream to retrieve blob data
InputStream instream = blob.getBinaryStream(offset);
// Create temporary buffer for read
byte[] buffer = new byte[10];
// length of bytes read
int length = 0;
// Fetch data
while ((length = instream.read(buffer)) != -1)
{
System.out.print("Read " + length + " bytes: ");

for (int i=0; i<length; i++)
System.out.print(buffer[i]+" ");
System.out.println();
}

// Close input stream
instream.close();
}

// Utility function to put data in a Clob
static void fillClob (Connection conn, CLOB clob, long offset, long length)
throws Exception
{
Writer outstream = clob.setCharacterStream(offset);

int i = 0;
int chunk = 10;

while (i < length)
{
outstream.write("aaaaaaaaaa", 0, chunk);

i += chunk;
if (length - i < chunk)
chunk = (int) length - i;
}
outstream.close();
}

// Utility function to put data in a Blob
static void fillBlob (Connection conn, BLOB blob, long offset, long length)
throws Exception
{
OutputStream outstream = blob.setBinaryStream(offset);

int i = 0;
int chunk = 10;

byte [] data = { 1, 1, 1, 1, 1, 1, 1, 1, 1, 1 };

while (i < length)
{
outstream.write(data, 0, chunk);

i += chunk;
if (length - i < chunk)
chunk = (int) length - i;
}
outstream.close();
}
}

JDBC and Empty LOBs

An empty BLOB can be created from the following API from oracle.sql.BLOB:

public static BLOB empty_lob () throws SQLException

Similarly, the following API from oracle.sql.CLOB creates an empty CLOB:

public static CLOB empty_lob () throws SQLException

Empty LOB instances are created by JDBC drivers without making database round trips. Empty LOBs can be used in the following cases:

- "set" APIs of PreparedStatement

- "update" APIs of updatable result set

- attribute value of STRUCTs

- element value of ARRAYs

Note:

Empty LOBs are special marker LOBs but not real LOB values.

JDBC applications cannot read or write to empty LOBs created from the preceding APIs. An ORA-17098 "Invalid empty lob operation" results if your application attempts to read/write to an empty LOB.

Oracle Provider for OLE DB (OraOLEDB)

Oracle Provider for OLE DB (OraOLEDB) offers high performance and efficient access to Oracle data for OLE DB and ADO developers. Developers programming with Visual Basic, C++, or any COM client can use OraOLEDB to access Oracle databases.

OraOLEDB is an OLE DB provider for Oracle. It offers high performance and efficient access to Oracle data including LOBs, and also allows updates to certain LOB types.

The following LOB types are supported by OraOLEDB:

- For Persistent LOBs. READ/WRITE through the rowset.

- For BFILEs. READ-ONLY through the rowset.

- Temporary LOBs are not supported through the rowset.

See Also:

Oracle Provider for OLE DB Developer's Guide

Overview of Oracle Data Provider for .NET (ODP.NET)

Oracle Data Provider for .NET (ODP.NET) is an implementation of a data provider for the Oracle database. ODP.NET uses Oracle native APIs to offer fast and reliable access to Oracle data and features from any .NET application. ODP.NET also uses and inherits classes and interfaces available in the Microsoft .NET Framework Class Library. The ODP.NET supports the following LOBs as native datatypes with .NET: BLOB, CLOB, NCLOB, and BFILE.

See Also:

Oracle Data Provider for .NET Developer's Guide

7 Performance Guidelines

This chapter contains these topics:

- LOB Performance Guidelines

- Moving Data to LOBs in a Threaded Environment

- LOB Access Statistics

LOB Performance Guidelines

This section describes performance guidelines for applications that use LOB datatypes.

Chunk Size

A chunk is one or more Oracle blocks. You can specify the chunk size for the LOB when creating the table that contains the LOB. This corresponds to the data size used by Oracle Database when accessing or modifying the LOB value. Part of the chunk is used to store system-related information and the rest stores the LOB value. The API you are using has a function that returns the amount of space used in the LOB chunk to store the LOB value. In PL/SQL use DBMS_LOB.GETCHUNKSIZE. In OCI, use OCILobGetChunkSize().

Performance Guidelines for Small LOBs

If most LOBs in your database tables are small in size—8K bytes or less—and only a few rows have LOBs larger than 8K bytes, then use the following guidelines to maximize database performance:

- Use ENABLE STORAGE IN ROW

- Set the DB_BLOCK_SIZE initialization parameter to 8K bytes and use a chunk size of 8K bytes

- See "LOB Storage" information on tuning other parameters such as CACHE, PCTVERSION, and CHUNK for the LOB segment.

General Performance Guidelines

Use the following guidelines to achieve maximum performance with LOBs:

- When Possible, Read/Write Large Data Chunks at a Time: Because LOBs are big, you can obtain the best performance by reading and writing large pieces of a LOB value at a time. This helps in several respects:

a. If accessing the LOB from the client side and the client is at a different node than the server, then large reads/writes reduce network overhead.

b. If using the NOCACHE option, then each small read/write incurs an I/O. Reading/writing large quantities of data reduces the I/O.

c. Writing to the LOB creates a new version of the LOB chunk. Therefore, writing small amounts at a time will incur the cost of a new version for each small write. If logging is on, then the chunk is also stored in the redo log.

- Use LOB Buffering to Read/Write Small Chunks of Data: If you need to read/write small pieces of LOB data on the client, then use LOB buffering — see OCILobEnableBuffering(), OCILobDisableBuffering(), OCILobFlushBuffer(), OCILobWrite2(), OCILobRead2(). Basically, turn on LOB buffering before reading/writing small pieces of LOB data.

See Also:

"LOB Buffering Subsystem" for more information on LOB buffering.

- Use OCILobRead2() and OCILobWrite2() with Callback: So that data is streamed to and from the LOB. Ensure the length of the entire write is set in the amount parameter on input. Whenever possible, read and write in multiples of the LOB chunk size.

- Use a Checkout/Check-in Model for LOBs: LOBs are optimized for the following operations:

- SQL UPDATE which replaces the entire LOB value

- Copy the entire LOB data to the client, modify the LOB data on the client side, copy the entire LOB data back to the database. This can be done using OCILobRead2() and OCILobWrite2() with streaming.

- Commit changes frequently.

Temporary LOB Performance Guidelines

In addition to the guidelines described earlier under "LOB Performance Guidelines" on LOB performance in general, here are some guidelines for using temporary LOBs:

- Use a separate temporary tablespace for temporary LOB storage instead of the default system tablespace. This avoids device contention when copying data from persistent LOBs to temporary LOBs.

If you use the newly provided enhanced SQL semantics functionality in your applications, then there will be many more temporary LOBs created silently in SQL and PL/SQL than before. Ensure that temporary tablespace for storing these temporary LOBs is large enough for your applications. In particular, these temporary LOBs are silently created when you use the following:

- SQL functions on LOBs

- PL/SQL built-in character functions on LOBs

- Variable assignments from VARCHAR2/RAW to CLOBs/BLOBs, respectively.

- Perform a LONG-to-LOB migration

- In PL/SQL, use NOCOPY to pass temporary LOB parameters by reference whenever possible. Refer to the Oracle Database PL/SQL User's Guide and Reference, for more information on passing parameters by reference and parameter aliasing.

- Take advantage of buffer cache on temporary LOBs. Temporary LOBs created with the CACHE parameter set to true move through the buffer cache. Otherwise temporary LOBs are read directly from, and written directly to, disk.

- For optimal performance, temporary LOBs use reference on read, copy on write semantics. When a temporary LOB locator is assigned to another locator, the physical LOB data is not copied. Subsequent READ operations using either of the LOB locators refer to the same physical LOB data. On the first WRITE operation after the assignment, the physical LOB data is copied in order to preserve LOB value semantics, that is, to ensure that each locator points to a unique LOB value. This performance consideration mainly applies to the PL/SQL and OCI environments.

In PL/SQL, reference on read, copy on write semantics are illustrated as follows:

LOCATOR1 BLOB;
LOCATOR2 BLOB;
DBMS_LOB.CREATETEMPORARY (LOCATOR1,TRUE,DBMS_LOB.SESSION);

-- LOB data is not copied in this assignment operation:
LOCATOR2 := LOCATOR;
-- These read operations refer to the same physical LOB copy:
DBMS_LOB.READ(LOCATOR1, ...);
DBMS_LOB.GETLENGTH(LOCATOR2, ...);

-- A physical copy of the LOB data is made on WRITE:
DBMS_LOB.WRITE(LOCATOR2, ...);

In OCI, to ensure value semantics of LOB locators and data, OCILobLocatorAssign() is used to copy temporary LOB locators as well as the LOB Data. OCILobLocatorAssign() does not make a round trip to the server. The physical temporary LOB copy is made when LOB updates happen in the same round trip as the LOB update API as illustrated in the following:

OCILobLocator *LOC1;
OCILobLocator *LOC2;
OCILobCreateTemporary(... LOC1, ... TRUE,OCI_DURATION_SESSION);

/* No round-trip is incurred in the following call. */
OCILobLocatorAssign(... LOC1, LOC2);

/* Read operations refer to the same physical LOB copy. */
OCILobRead2(... LOC1 ...)

/* One round-trip is incurred to make a new copy of the
* LOB data and to write to the new LOB copy.
*/
OCILobWrite2(... LOC1 ...)

/* LOC2 does not see the same LOB data as LOC1. */
OCILobRead2(... LOC2 ...)

If LOB value semantics are not intended, then you can use C pointers to achieve reference semantics as illustrated in the following:

OCILobLocator *LOC1;
OCILobLocator *LOC2;
OCILobCreateTemporary(... LOC1, ... TRUE,OCI_DURATION_SESSION);

/* Pointer is copied. LOC1 and LOC2 refer to the same LOB data. */
LOC2 = LOC1;

/* Write to LOC2. */
OCILobWrite2(...LOC2...)

/* LOC1 will see the change made to LOC2. */
OCILobRead2(...LOC1...)

- Use OCI_OBJECT mode for temporary LOBs

To improve the performance of temporary LOBs on LOB assignment, use OCI_OBJECT mode for OCILobLocatorAssign(). In OCI_OBJECT mode, the database tries to minimize the number of deep copies to be done. Hence, after OCILobLocatorAssign() is done on a source temporary LOB in OCI_OBJECT mode, the source and the destination locators will point to the same LOB until any modification is made through either LOB locator.

- Free up temporary LOBs returned from SQL queries and PL/SQL programs.

In PL/SQL, C (OCI), Java and other programmatic interfaces, SQL query results or PL/SQL program executions return temporary LOBs for operation/function calls on LOBs. For example:

SELECT substr(CLOB_Column, 4001, 32000) FROM ...

If the query is executed in PL/SQL, then the returned temporary LOBs automatically get freed at the end of a PL/SQL program block. You can also explicitly free the temporary LOBs any time. In OCI and Java, the returned temporary LOB must be freed by the user explicitly.

Without proper deallocation of the temporary LOBs returned from SQL queries, temporary tablespace gets filled up steadily and you could observe performance degradation.

Performance Considerations for SQL Semantics and LOBs

Be aware of the following performance issues when using SQL semantics with LOBs:

- Ensure that your temporary tablespace is large enough to accommodate LOBs stored out-of-line. Persistent LOBs that are greater than 3964 bytes in size are stored outside of the LOB column.

- When possible, free unneeded temporary LOB instances. Unless you explicitly free a temporary LOB instance, the LOB remains in existence while your application is executing. More specifically, the instance exists while the scope in which the LOB was declared is executing.

See Also:

Chapter 9, "SQL Semantics and LOBs" for details on SQL semantics support for LOBs.

Moving Data to LOBs in a Threaded Environment

There two procedures that you can use to move data to LOBs in a threaded environment, one of which should be avoided.

Procedure to Avoid

The following sequence requires a new connection when using a threaded environment, adversely affects performance, and is not recommended:

1. Create an empty (non-NULL) LOB

2. Perform INSERT using the empty LOB

3. SELECT-FOR-UPDATE of the row just entered

4. Move data into the LOB

5. Do a COMMIT. This releases the SELECT-FOR-UPDATE locks and makes the LOB data persistent.

Recommended Procedure

Note:

- There is no need to create an empty LOB in this procedure.

- You can use the RETURNING clause as part of the INSERT/UPDATE statement to return a locked LOB locator. This eliminates the need for doing a SELECT-FOR-UPDATE, as mentioned in step 3.

The recommended procedure is as follows:

1. INSERT an empty LOB, RETURNING the LOB locator.

2. Move data into the LOB using this locator.

3. COMMIT. This releases the SELECT-FOR-UPDATE locks, and makes the LOB data persistent.

Alternatively, you can insert more than 4000 byte of data directly for the LOB columns or LOB attributes.

LOB Access Statistics

Since Oracle Database 10g Release 2, three session-level statistics specific to LOBs are available to users: LOB reads, LOB writes, and LOB writes unaligned. Session statistics are accessible through the V$MYSTAT, V$SESSTAT, and V$SYSSTAT dynamic performance views. To query these views, the user needs to be granted the privileges SELECT_CATALOG_ROLE, SELECT ON SYS.V_$MYSTAT view, and SELECT ON SYS.V_$STATNAME view.

LOB reads is defined as the number of LOB API read operations performed in the session/system. A single LOB API read may correspond to multiple physical/logical disk block reads.

LOB writes is defined as the number of LOB API write operations performed in the session/system. A single LOB API write may correspond to multiple physical/logical disk block writes.

LOB writes unaligned is defined as the number of LOB API write operations whose start offset or buffer size is not aligned to the internal chunk size of the LOB. Writes aligned to chunk boundaries are the most efficient write operations. The internal chunk size of a LOB is available through the LOB API (for example, using PL/SQL, by DBMS_LOB.GETCHUNKSIZE()).

The following simple example demonstrates how LOB session statistics are updated as the user performs read/write operations on LOBs.

It is important to note that session statistics are aggregated across operations to all LOBs accessed in a session; the statistics are not separated or categorized by objects (that is, table, column, segment, object numbers, and so on).

In these examples, you reconnect to the database for each demonstration to clear the V$MYSTAT. This allows you to see how the lob statistics change for the specific operation you are testing, without the potentially obscuring effect of past LOB operations within the same session.

See also:

Oracle Database Reference, appendix E, "Statistics Descriptions"

Example of Retrieving LOB Access Statistics

This example was created for retrieving LOB access statistics.

rem
rem Set up the user
rem

CONNECT / AS SYSDBA;
SET ECHO ON;
GRANT SELECT_CATALOG_ROLE TO pm;
GRANT SELECT ON sys.v_$mystat TO pm;
GRANT SELECT ON sys.v_$statname TO pm;

rem
rem Create a simplified view for statistics queries
rem

CONNECT pm/pm;
SET ECHO ON;

DROP VIEW mylobstats;
CREATE VIEW mylobstats
AS
SELECT  SUBSTR(n.name,1,20) name,
m.value             value
FROM    v$mystat    m,
v$statname  n
WHERE   m.statistic# = n.statistic#
AND n.name LIKE 'lob%';

rem
rem Create a test table
rem

DROP TABLE t;
CREATE TABLE t (i NUMBER, c CLOB)
lob(c) STORE AS (DISABLE STORAGE IN ROW);

rem
rem Populate some data
rem
rem This should result in unaligned writes, one for
rem each row/lob populated.
rem

CONNECT pm/pm;
SELECT * FROM mylobstats;
INSERT INTO t VALUES (1, 'a');
INSERT INTO t VALUES (2, rpad('a',4000,'a'));
COMMIT;
SELECT * FROM mylobstats;

rem
rem Get the lob length
rem
rem Computing lob length does not read lob data, no change
rem in read/write stats.
rem

CONNECT pm/pm;
SELECT * FROM mylobstats;
SELECT LENGTH(c) FROM t;
SELECT * FROM mylobstats;

rem
rem Read the lobs
rem
rem Lob reads are performed, one for each lob in the table.
rem

CONNECT pm/pm;
SELECT * FROM mylobstats;
SELECT * FROM t;
SELECT * FROM mylobstats;

rem
rem Read and manipulate the lobs (via temporary lobs)
rem
rem The use of complex operators like "substr()" results in
rem the implicit creation and use of temporary lobs. operations
rem on temporary lobs also update lob statistics.
rem

CONNECT pm/pm;
SELECT * FROM mylobstats;
SELECT substr(c, length(c), 1) FROM t;
SELECT substr(c, 1, 1) FROM t;
SELECT * FROM mylobstats;

rem
rem Perform some aligned overwrites
rem
rem Only lob write statistics are updated since both the
rem byte offset of the write, and the size of the buffer
rem being written are aligned on the lob chunksize.
rem

CONNECT pm/pm;
SELECT * FROM mylobstats;
DECLARE
loc     CLOB;
buf     LONG;
chunk   NUMBER;
BEGIN
SELECT c INTO loc FROM t WHERE i = 1
FOR UPDATE;

chunk := DBMS_LOB.GETCHUNKSIZE(loc);
buf   := rpad('b', chunk, 'b');

-- aligned buffer length and offset
DBMS_LOB.WRITE(loc, chunk, 1, buf);
DBMS_LOB.WRITE(loc, chunk, 1+chunk, buf);
COMMIT;
END;
/
SELECT * FROM mylobstats;

rem
rem Perform some unaligned overwrites
rem
rem Both lob write and lob unaligned write statistics are
rem updated since either one or both of the write byte offset
rem and buffer size are unaligned with the lob's chunksize.
rem

CONNECT pm/pm;
SELECT * FROM mylobstats;
DECLARE
loc CLOB;
buf LONG;
BEGIN
SELECT c INTO loc FROM t WHERE i = 1
FOR UPDATE;

buf := rpad('b', DBMS_LOB.GETCHUNKSIZE(loc), 'b');

-- unaligned buffer length
DBMS_LOB.WRITE(loc, DBMS_LOB.GETCHUNKSIZE(loc)-1, 1, buf);

-- unaligned start offset
DBMS_LOB.WRITE(loc, DBMS_LOB.GETCHUNKSIZE(loc), 2, buf);

-- unaligned buffer length and start offset
DBMS_LOB.WRITE(loc, DBMS_LOB.GETCHUNKSIZE(loc)-1, 2, buf);

COMMIT;
END;
/
SELECT * FROM mylobstats;
DROP TABLE t;
DROP VIEW mylobstats;

CONNECT / AS SYSDBA
REVOKE SELECT_CATALOG_ROLE FROM pm;
REVOKE SELECT ON sys.v_$mystat FROM pm;
REVOKE SELECT ON sys.v_$statname FROM pm;

QUIT;

Part III

SQL Access to LOBs

This part describes SQL semantics for LOBs supported in the SQL and PL/SQL environments.

This part contains these chapters:

- Chapter 8, "DDL and DML Statements with LOBs"

- Chapter 9, "SQL Semantics and LOBs"

- Chapter 10, "PL/SQL Semantics for LOBs"

- Chapter 11, "Migrating Columns from LONGs to LOBs"

8 DDL and DML Statements with LOBs

This chapter contains these topics:

- Creating a Table Containing One or More LOB Columns

- Creating a Nested Table Containing a LOB

- Inserting a Row by Selecting a LOB From Another Table

- Inserting a LOB Value Into a Table

- Inserting a Row by Initializing a LOB Locator Bind Variable

- Updating a LOB with EMPTY_CLOB() or EMPTY_BLOB()

- Updating a Row by Selecting a LOB From Another Table

See Also:

For guidelines on how to INSERT into a LOB when binds of more than 4000 bytes are involved, see the following sections in "Binds of All Sizes in INSERT and UPDATE Operations".

Creating a Table Containing One or More LOB Columns

This section describes how to create a table containing one or more LOB columns.

When you use functions, EMPTY_BLOB() and EMPTY_CLOB(), the resulting LOB is initialized, but not populated with data. Also note that LOBs that are empty are not NULL.

See Also:

Oracle Database SQL Reference for a complete specification of syntax for using LOBs in CREATE TABLE and ALTER TABLE with:

- BLOB, CLOB, NCLOB and BFILE columns

- EMPTY_BLOB and EMPTY_CLOB functions

- LOB storage clause for persistent LOB columns, and LOB attributes of embedded objects

Scenario

These examples use the following Sample Schemas:

- Human Resources (HR)

- Order Entry (OE)

- Product Media (PM)

Note that the HR and OE schemas must exist before the PM schema is created. For details on these schemas, refer to Oracle Database Sample Schemas.

Note:

Because you can use SQL DDL directly to create a table containing one or more LOB columns, it is not necessary to use the DBMS_LOB package.

/*  Setup script for creating Print_media,
Online_media and associated structures
*/

DROP USER pm CASCADE;
DROP DIRECTORY ADPHOTO_DIR;
DROP DIRECTORY ADCOMPOSITE_DIR;
DROP DIRECTORY ADGRAPHIC_DIR;
DROP INDEX onlinemedia CASCADE CONSTRAINTS;
DROP INDEX printmedia CASCADE CONSTRAINTS;
DROP TABLE online_media CASCADE CONSTRAINTS;
DROP TABLE print_media CASCADE CONSTRAINTS;
DROP TYPE textdoc_typ;
DROP TYPE textdoc_tab;
DROP TYPE adheader_typ;
DROP TABLE adheader_typ;
CREATE USER pm;
GRANT CONNECT, RESOURCE to pm;

CREATE DIRECTORY ADPHOTO_DIR AS '/tmp/';
CREATE DIRECTORY ADCOMPOSITE_DIR AS '/tmp/';
CREATE DIRECTORY ADGRAPHIC_DIR AS '/tmp/';
CREATE DIRECTORY media_dir AS '/tmp/';
GRANT READ ON DIRECTORY ADPHOTO_DIR to pm;
GRANT READ ON DIRECTORY ADCOMPOSITE_DIR to pm;
GRANT READ ON DIRECTORY ADGRAPHIC_DIR to pm;
GRANT READ ON DIRECTORY media_dir to pm;

CONNECT pm/pm  (or &pass);
COMMIT;

CREATE TABLE a_table (blob_col BLOB);

CREATE TYPE adheader_typ AS OBJECT (
header_name    VARCHAR2(256),
creation_date  DATE,
header_text    VARCHAR(1024),
logo           BLOB );

CREATE TYPE textdoc_typ AS OBJECT (
document_typ   VARCHAR2(32),
formatted_doc  BLOB);

CREATE TYPE Textdoc_ntab AS TABLE of textdoc_typ;

CREATE TABLE adheader_tab of adheader_typ (
Ad_finaltext DEFAULT EMPTY_CLOB(), CONSTRAINT
Take CHECK (Take IS NOT NULL),  DEFAULT NULL);

CREATE TABLE online_media
( product_id  NUMBER(6),
product_photo ORDSYS.ORDImage,
product_photo_signature ORDSYS.ORDImageSignature,
product_thumbnail ORDSYS.ORDImage,
product_video ORDSYS.ORDVideo,
product_audio ORDSYS.ORDAudio,
product_text CLOB,
product_testimonials ORDSYS.ORDDoc);

CREATE UNIQUE INDEX onlinemedia_pk
ON online_media (product_id);

ALTER TABLE online_media
ADD (CONSTRAINT onlinemedia_pk
PRIMARY KEY (product_id), CONSTRAINT loc_c_id_fk
FOREIGN KEY (product_id)  REFERENCES oe.product_information(product_id)
);

CREATE TABLE print_media
(product_id NUMBER(6),
ad_id NUMBER(6),
ad_composite BLOB,
ad_sourcetext CLOB,
ad_finaltext CLOB,
ad_fktextn NCLOB,
ad_testdocs_ntab textdoc_tab,
ad_photo BLOB,
ad_graphic BFILE,
ad_header adheader_typ,
press_release LONG) NESTED TABLE ad_textdocs_ntab STORE AS textdocs_nestedtab;

CREATE UNIQUE INDEX printmedia_pk
ON print_media (product_id, ad_id);

ALTER TABLE print_media
ADD (CONSTRAINT printmedia_pk
PRIMARY KEY (product_id, ad_id),
CONSTRAINT printmedia_fk FOREIGN KEY (product_id)
REFERENCES oe.product_information(product_id)
);

Creating a Nested Table Containing a LOB

This section describes how to create a nested table containing a LOB.

You must create the object type that contains the LOB attributes before you create a nested table based on that object type. In the example that follows, table Print_media contains nested table ad_textdoc_ntab that has type textdoc_tab. This type uses two LOB datatypes:

- BFILE - an advertisement graphic

- CLOB - an advertisement transcript

The actual embedding of the nested table is accomplished when the structure of the containing table is defined. In our example, this is effected by the NESTED TABLE statement when the Print_media table is created as shown in the following example:

/* Create type textdoc_typ as the base type
for the nested table textdoc_ntab,
where textdoc_ntab contains a LOB:
*/
CREATE TYPE textdoc_typ AS OBJECT
(
document_typ    VARCHAR2(32),
formatted_doc   BLOB
);
/

/* The type has been created. Now you need a */
/* nested table of that type to embed in */
/* table Print_media, so: */
CREATE TYPE textdoc_ntab AS TABLE of textdoc_typ;
/

CREATE TABLE textdoc_ntable (
id NUMBER,
ntab_col textdoc_ntab)
NESTED TABLE ntab_col STORE AS textdoc_nestedtab;

DROP TYPE textdoc_typ force;
DROP TYPE textdoc_ntab;
DROP TABLE textdoc_ntable;

See Also:

- "Creating a Table Containing One or More LOB Columns"

- Oracle Database SQL Reference, "Chapter 7, SQL Statements" — CREATE TABLE.

Inserting a Row by Selecting a LOB From Another Table

This section describes how to insert a row containing a LOB as SELECT.

Note:

Persistent LOB types BLOB, CLOB, and NCLOB, use copy semantics, as opposed to reference semantics that apply to BFILEs. When a BLOB, CLOB, or NCLOB is copied from one row to another in the same table or a different table, the actual LOB value is copied, not just the LOB locator.

For LOBs, one of the advantages of using an object-relational approach is that you can define a type as a common template for related tables. For instance, it makes sense that both the tables that store archival material and working tables that use those libraries, share a common structure.

For example, assuming Print_media and Online_media have identical schemas. The statement creates a new LOB locator in table Print_media. It also copies the LOB data from Online_media to the location pointed to by the new LOB locator inserted in table Print_media.

The following code fragment is based on the fact that the table Online_media is of the same type as Print_media referenced by the ad_textdocs_ntab column of table Print_media. It inserts values into the library table, and then inserts this same data into Print_media by means of a SELECT.

/* Store records in the archive table Online_media: */
INSERT INTO Online_media
VALUES (3060, NULL, NULL, NULL, NULL,
'some text about this CRT Monitor', NULL);

/* Insert values into Print_media by selecting from Online_media: */
INSERT INTO Print_media (product_id, ad_id, ad_sourcetext)
(SELECT product_id, 11001, product_text
FROM Online_media WHERE product_id = 3060);

See Also:

- Oracle Database SQL Reference, "Chapter 7, SQL Statements" — INSERT.

- Oracle Database Sample Schemas for a description of the PM Schema and the Print_media table used in this example.

Inserting a LOB Value Into a Table

This section describes how to insert a LOB value using EMPTY_CLOB() or EMPTY_BLOB().

Usage Notes

Here are guidelines for inserting LOBs:

Before inserting, Make the LOB Column Non-Null

Before you write data to a persistent LOB, make the LOB column non-NULL; that is, the LOB column must contain a locator that points to an empty or populated LOB value. You can initialize a BLOB column value by using the function EMPTY_BLOB() as a default predicate. Similarly, a CLOB or NCLOB column value can be initialized by using the function EMPTY_CLOB().

You can also initialize a LOB column with a character or raw string less than 4000 bytes in size. For example:

INSERT INTO Print_media (product_id, ad_id, ad_sourcetext)
VALUES (1, 1, 'This is a One Line Advertisement');

Note that you can also perform this initialization during the CREATE TABLE operation. See "Creating a Table Containing One or More LOB Columns" for more information.

These functions are special functions in Oracle SQL, and are not part of the DBMS_LOB package.

/* In the new row of table Print_media,
the columns ad_sourcetext and ad_fltextn are initialized using EMPTY_CLOB(),
the columns ad_composite and ad_photo are initialized using EMPTY_BLOB(),
the column formatted-doc in the nested table is initialized using
EMPTY_BLOB(),
the column logo in the column object is initialized using EMPTY_BLOB(): */
INSERT INTO Print_media
VALUES (3060,11001, EMPTY_BLOB(), EMPTY_CLOB(),EMPTY_CLOB(),EMPTY_CLOB(),
textdoc_tab(textdoc_typ ('HTML', EMPTY_BLOB())), EMPTY_BLOB(), NULL,
adheader_typ('any header name', <any date>, 'ad header text goes here',
EMPTY_BLOB()),
'Press release goes here');

Inserting a Row by Initializing a LOB Locator Bind Variable

This section gives examples of how to insert a row by initializing a LOB locator bind variable.

Preconditions

Before you can insert a row using this technique, the following conditions must be met:

- The table containing the source row must exist.

- The destination table must exist.

For details on creating tables containing LOB columns, see Chapter 4, "LOBs in Tables".

Usage Notes

For guidelines on how to INSERT and UPDATE a row containing a LOB when binds of more than 4000 bytes are involved, see "Binds of All Sizes in INSERT and UPDATE Operations".

Syntax

See the following syntax references for details on using this operation in each programmatic environment:

- SQL: Oracle Database SQL Reference, "Chapter 7, SQL Statements" — INSERT

- C (OCI): Oracle Call Interface Programmer's Guide "Relational Functions" — LOB Functions.

- C++ (OCCI): Oracle C++ Call Interface Programmer's Guide

- COBOL (Pro*COBOL) Pro*COBOL Programmer's Guide for information on LOBs, usage notes on LOB Statements, and embedded SQL and precompiler directives — INSERT.

- C/C++ (Pro*C/C++): Pro*C/C++ Programmer's Guide Appendix F, "Embedded SQL Statements and Directives" — INSERT

- Visual Basic (OO4O) (Oracle Objects for OLE (OO4O) Online Help): From Help Topics, Contents tab, select OO4O Automation Server > Objects > Oradynaset

- Java (JDBC): Oracle Database JDBC Developer's Guide and Reference Chapter 7, "Working With LOBs" — Creating and Populating a BLOB or CLOB Column.

Examples

Examples for this use case are provided in the following programmatic environments:

- PL/SQL: Inserting a Row by Initializing a LOB Locator Bind Variable

- C (OCI): Inserting a Row by Initializing a LOB Locator Bind Variable

- C++ (OCCI): No example is provided with this release.

- COBOL (Pro*COBOL): Inserting a Row by Initializing a LOB Locator Bind Variable

- C/C++ (Pro*C/C++): Inserting a Row by Initializing a LOB Locator Bind Variable

- Visual Basic (OO4O): Inserting a Row by Initializing a LOB Locator Bind Variable

- Java (JDBC): Inserting a Row by Initializing a LOB Locator Bind Variable

PL/SQL: Inserting a Row by Initializing a LOB Locator Bind Variable

/* This file is installed in the following path when you install */
/* the database: $ORACLE_HOME/rdbms/demo/lobs/plsql/linsert.sql */

/* inserting a row through an insert statement */

CREATE OR REPLACE PROCEDURE insertLOB_proc (Lob_loc IN BLOB) IS
BEGIN
/* Insert the BLOB into the row */
DBMS_OUTPUT.PUT_LINE('------------ LOB INSERT EXAMPLE ------------');
INSERT INTO print_media (product_id, ad_id, ad_photo)
values (3106, 60315, Lob_loc);
END;
/

C (OCI): Inserting a Row by Initializing a LOB Locator Bind Variable

/* This file is installed in the following path when you install */
/* the database: $ORACLE_HOME/rdbms/demo/lobs/oci/linsert.c */

/* Insert the Locator into table using Bind Variables. */
#include <oratypes.h>
#include <lobdemo.h>
void insertLOB_proc(OCILobLocator *Lob_loc, OCIEnv *envhp,
OCIError *errhp, OCISvcCtx *svchp, OCIStmt *stmthp)
{
int            product_id;
OCIBind       *bndhp3;
OCIBind       *bndhp2;
OCIBind       *bndhp1;
text          *insstmt =
(text *) "INSERT INTO Print_media (product_id, ad_id, ad_sourcetext) \
VALUES (:1, :2, :3)";

printf ("----------- OCI Lob Insert Demo --------------\n");
/* Insert the locator into the Print_media table with product_id=3060 */
product_id = (int)3060;

/* Prepare the SQL statement */
checkerr (errhp, OCIStmtPrepare(stmthp, errhp, insstmt, (ub4)
strlen((char *) insstmt),
(ub4) OCI_NTV_SYNTAX, (ub4)OCI_DEFAULT));

/* Binds the bind positions */
checkerr (errhp, OCIBindByPos(stmthp, &bndhp1, errhp, (ub4) 1,
(void *) &product_id, (sb4) sizeof(product_id),
SQLT_INT, (void *) 0, (ub2 *)0, (ub2 *)0,
(ub4) 0, (ub4 *) 0, (ub4) OCI_DEFAULT));

checkerr (errhp, OCIBindByPos(stmthp, &bndhp1, errhp, (ub4) 2,
(void *) &product_id, (sb4) sizeof(product_id),
SQLT_INT, (void *) 0, (ub2 *)0, (ub2 *)0,
(ub4) 0, (ub4 *) 0, (ub4) OCI_DEFAULT));

checkerr (errhp, OCIBindByPos(stmthp, &bndhp2, errhp, (ub4) 3,
(void *) &Lob_loc, (sb4) 0,  SQLT_CLOB,
(void *) 0, (ub2 *)0, (ub2 *)0,
(ub4) 0, (ub4 *) 0, (ub4) OCI_DEFAULT));

/* Execute the SQL statement */
checkerr (errhp, OCIStmtExecute(svchp, stmthp, errhp, (ub4) 1, (ub4) 0,
(CONST OCISnapshot*) 0, (OCISnapshot*) 0,
(ub4) OCI_DEFAULT));
}

COBOL (Pro*COBOL): Inserting a Row by Initializing a LOB Locator Bind Variable

* This file is installed in the following path when you install
* the database: $ORACLE_HOME/rdbms/demo/lobs/procob/linsert.pco

IDENTIFICATION DIVISION.
PROGRAM-ID. INSERT-LOB.
ENVIRONMENT DIVISION.
DATA DIVISION.
WORKING-STORAGE SECTION.

01 BLOB1 SQL-BLOB.
01  USERID   PIC X(11) VALUES "PM/PM".
EXEC SQL INCLUDE SQLCA END-EXEC.

PROCEDURE DIVISION.
INSERT-LOB.

EXEC SQL WHENEVER SQLERROR DO PERFORM SQL-ERROR END-EXEC.
EXEC SQL CONNECT :USERID END-EXEC.
* Initialize the BLOB locator
EXEC SQL ALLOCATE :BLOB1 END-EXEC.
* Populate the LOB
EXEC SQL WHENEVER NOT FOUND GOTO END-OF-BLOB END-EXEC.
EXEC SQL
SELECT AD_PHOTO INTO :BLOB1 FROM PRINT_MEDIA
WHERE PRODUCT_ID = 2268 AND AD_ID = 21001 END-EXEC.

* Insert the value with PRODUCT_ID of 3060
EXEC SQL
INSERT INTO PRINT_MEDIA (PRODUCT_ID, AD_PHOTO)
VALUES (3060, 11001, :BLOB1)END-EXEC.

* Free resources held by locator
END-OF-BLOB.
EXEC SQL WHENEVER NOT FOUND CONTINUE END-EXEC.
EXEC SQL FREE :BLOB1 END-EXEC.
EXEC SQL ROLLBACK WORK RELEASE END-EXEC.
STOP RUN.

SQL-ERROR.
EXEC SQL WHENEVER SQLERROR CONTINUE END-EXEC.
DISPLAY " ".
DISPLAY "ORACLE ERROR DETECTED:".
DISPLAY " ".
DISPLAY SQLERRMC.
EXEC SQL ROLLBACK WORK RELEASE END-EXEC.
STOP RUN.

C/C++ (Pro*C/C++): Inserting a Row by Initializing a LOB Locator Bind Variable

/* This file is installed in the following path when you install */
/* the database: $ORACLE_HOME/rdbms/demo/lobs/proc/linsert.pc */

#include <oci.h>
#include <stdio.h>
#include <sqlca.h>

void Sample_Error()
{
EXEC SQL WHENEVER SQLERROR CONTINUE;
printf("%.*s\n", sqlca.sqlerrm.sqlerrml, sqlca.sqlerrm.sqlerrmc);
EXEC SQL ROLLBACK WORK RELEASE;
exit(1);
}

void insertUseBindVariable_proc(Rownum, Lob_loc)
int Rownum, Rownum2;
OCIBlobLocator *Lob_loc;
{
EXEC SQL WHENEVER SQLERROR DO Sample_Error();
EXEC SQL INSERT INTO Print_media (product_id, ad_id, ad_photo)
VALUES (:Rownum, :Rownum2, :Lob_loc);
}
void insertBLOB_proc()
{
OCIBlobLocator *Lob_loc;

/* Initialize the BLOB Locator: */
EXEC SQL ALLOCATE :Lob_loc;

/* Select the LOB from the row where product_id = 2268 and ad_id=21001: */
EXEC SQL SELECT ad_photo INTO :Lob_loc
FROM Print_media WHERE product_id = 2268 AND ad_id = 21001;

/* Insert into the row where product_id = 3106 and ad_id = 13001: */
insertUseBindVariable_proc(3106, 13001, Lob_loc);

/* Release resources held by the locator: */
EXEC SQL FREE :Lob_loc;
}

void main()
{
char *samp = "pm/pm";
EXEC SQL CONNECT :pm;
insertBLOB_proc();
EXEC SQL ROLLBACK WORK RELEASE;
}

Visual Basic (OO4O): Inserting a Row by Initializing a LOB Locator Bind Variable

' This file is installed in the following path when you install
' the database: $ORACLE_HOME/rdbms/demo/lobs/vb/linsert.bas

Dim OraDyn as OraDynaset, OraPhoto1 as OraBLOB, OraPhotoClone as OraBLOB
Set OraDyn = OraDb.CreateDynaset(
"SELECT * FROM Print_media ORDER BY product_id", ORADYN_DEFAULT)
Set OraPhoto1 = OraDyn.Fields("ad_photo").Value
'Clone it for future reference
Set OraPhotoClone = OraPhoto1

'Go to Next row
OraDyn.MoveNext
'Lets update the current row and set the LOB to OraPhotoClone
OraDyn.Edit
Set OraPhoto1 = OraPhotoClone
OraDyn.Update

Java (JDBC): Inserting a Row by Initializing a LOB Locator Bind Variable

/* This file is installed in the following path when you install */
/* the database: $ORACLE_HOME/rdbms/demo/lobs/java/linsert.java */

// Core JDBC classes:
import java.sql.DriverManager;
import java.sql.Connection;
import java.sql.Statement;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

// Oracle Specific JDBC classes:
import oracle.sql.*;
import oracle.jdbc.driver.*;

public class linsert
{
public static void main (String args [])
throws Exception
{
// Load the Oracle JDBC driver
DriverManager.registerDriver (new oracle.jdbc.driver.OracleDriver ());
// Connect to the database:
Connection conn =
DriverManager.getConnection ("jdbc:oracle:oci8:@", "pm", "pm");

// It's faster when auto commit is off:
conn.setAutoCommit (false);

// Create a Statement:
Statement stmt = conn.createStatement ();
try
{
ResultSet rset = stmt.executeQuery (
"SELECT ad_photo FROM Print_media WHERE product_id = 3106 AND ad_id = 13001");
if (rset.next())
{
// retrieve the LOB locator from the ResultSet
BLOB adphoto_blob = ((OracleResultSet)rset).getBLOB (1);
OraclePreparedStatement ops =
(OraclePreparedStatement) conn.prepareStatement(
"INSERT INTO Print_media (product_id, ad_id, ad_photo) VALUES (2268, "
+ "21001, ?)");
ops.setBlob(1, adphoto_blob);
ops.execute();
conn.commit();
conn.close();
}
}
catch (SQLException e)
{
e.printStackTrace();
}
}
}

Updating a LOB with EMPTY_CLOB() or EMPTY_BLOB()

This section describes how to UPDATE a LOB with EMPTY_CLOB() or EMPTY_BLOB().

Note:

Performance improves when you update the LOB with the actual value, instead of using EMPTY_CLOB() or EMPTY_BLOB().

Preconditions

Before you write data to a persistent LOB, make the LOB column non-NULL; that is, the LOB column must contain a locator that points to an empty or populated LOB value. You can initialize a BLOB column value by using the function EMPTY_BLOB() as a default predicate. Similarly, a CLOB or NCLOB column value can be initialized by using the function EMPTY_CLOB().

You can also initialize a LOB column with a character or raw string less than 4000 bytes in size. For example:

UPDATE Print_media
SET ad_sourcetext = 'This is a One Line Story'
WHERE product_id = 2268;

You can perform this initialization during CREATE TABLE (see "Creating a Table Containing One or More LOB Columns") or, as in this case, by means of an INSERT.

The following example shows a series of updates using the EMPTY_CLOB operation to different data types.

UPDATE Print_media SET ad_sourcetext = EMPTY_CLOB()
WHERE product_id = 3060 AND ad_id = 11001;

UPDATE Print_media SET ad_fltextn = EMPTY_CLOB()
WHERE product_id = 3060 AND ad_id = 11001;

UPDATE Print_media SET ad_photo = EMPTY_BLOB()
WHERE product_id = 3060 AND ad_id = 11001;

See Also:

SQL: Oracle Database SQL Reference Chapter 7, "SQL Statements" — UPDATE

Updating a Row by Selecting a LOB From Another Table

This section describes how to use the SQL UPDATE AS SELECT statement to update a row containing a LOB column by selecting a LOB from another table.

To use this technique, you must update by means of a reference. For example, the following code updates data from online_media:

Rem Updating a row by selecting a LOB from another table (persistent LOBs)

UPDATE Print_media SET ad_sourcetext =
(SELECT * product_text FROM online_media WHERE product_id = 3060);
WHERE product_id = 3060 AND ad_id = 11001;

9 SQL Semantics and LOBs

This chapter describes SQL semantics that are supported for LOBs. These techniques allow you to use LOBs directly in SQL code and provide an alternative to using LOB-specific APIs for some operations.

This chapter contains these topics:

- Using LOBs in SQL

- SQL Functions and Operators Supported for Use with LOBs

- Implicit Conversion of LOB Datatypes in SQL

- Unsupported Use of LOBs in SQL

- VARCHAR2 and RAW Semantics for LOBs

See Also:

"Performance Considerations for SQL Semantics and LOBs".

Using LOBs in SQL

You can access CLOB and NCLOB datatypes using SQL VARCHAR2 semantics, such as SQL string operators and functions. (LENGTH functions can be used with BLOB datatypes as well as CLOB and NCLOBs.) These techniques are beneficial in the following situations:

- When performing operations on LOBs that are relatively small in size (up to about 100K bytes).

- After migrating your database from LONG columns to LOB datatypes, any SQL string functions, contained in your existing PL/SQL application, will continue to work after the migration.

SQL semantics are not recommended in the following situations:

- When you need to use advanced features such as random access and piecewise fetch, you should use LOB APIs.

- When performing operations on LOBs that are relatively large in size (greater than 1MB) using SQL semantics can impact performance. Using the LOB APIs is recommended in this situation.

Note:

SQL semantics are used with persistent and temporary LOBs. (SQL semantics do not apply to BFILE columns as BFILE is a read-only datatype.)

SQL Functions and Operators Supported for Use with LOBs

Many SQL operators and functions that take VARCHAR2 columns as arguments also accept LOB columns. The following list summarizes which categories of SQL functions and operators are supported for use with LOBs. Details on individual functions and operators are given in Table 9-1.

The following categories of SQL functions and operators are supported for use with LOBs:

- Concatenation

- Comparison

(Some comparison functions are not supported for use with LOBs.)

- Character functions

- Conversion

(Some conversion functions are not supported for use with LOBs.)

The following categories of functions are not supported for use with LOBs:

- Aggregate functions

Note that although pre-defined aggregate functions are not supported for use with LOBs, you can create user-defined aggregate functions to use with LOBs. See the Oracle Database Data Cartridge Developer's Guide for more information on user-defined aggregate functions.

- Unicode functions

Details on individual functions and operators are given in Table 9-1. This table lists SQL operators and functions that take VARCHAR2 types as operands or arguments, or return a VARCHAR2 value, and indicates in the "SQL" column which functions and operators are supported for CLOB and NCLOB datatypes. (The LENGTH function is also supported for the BLOB datatype.)

The DBMS_LOB PL/SQL package supplied with Oracle Database supports using LOBs with most of the functions listed in Table 9-1 as indicated in the "PL/SQL" column.

Note:

Operators and functions with "No" indicated in the SQL column of Table 9-1 do not work in SQL queries used in PL/SQL blocks - even though some of these operators and functions are supported for use directly in PL/SQL code.

Implicit Conversion of CLOB to CHAR Types

Functions designated as "CNV" in the SQL or PL/SQL column of Table 9-1 are performed by converting the CLOB to a character datatype, such as VARCHAR2. In the SQL environment, only the first 4K bytes of the CLOB are converted and used in the operation; in the PL/SQL environment, only the first 32K bytes of the CLOB are converted and used in the operation.

Table 9-1 SQL VARCHAR2 Functions and Operators on LOBs

Category

Operator / Function

SQL Example / Comments

SQL

PL/SQL

Concatenation

||, CONCAT()

Select clobCol || clobCol2 from tab;

Yes

Yes

Comparison

= , !=, >, >=, <, <=, <>, ^=

if clobCol=clobCol2 then...

No

Yes

Comparison

IN, NOT IN

if clobCol NOT IN (clob1, clob2, clob3) then...

No

Yes

Comparison

SOME, ANY, ALL

if clobCol < SOME (select clobCol2 from...) then...

No

N/A

Comparison

BETWEEN

if clobCol BETWEEN clobCol2 and clobCol3 then...

No

Yes

Comparison

LIKE [ESCAPE]

if clobCol LIKE '%pattern%' then...

Yes

Yes

Comparison

IS [NOT] NULL

where clobCol IS NOT NULL

Yes

Yes

Character Functions

INITCAP, NLS_INITCAP

select INITCAP(clobCol) from...

CNV

CNV

Character Functions

LOWER, NLS_LOWER, UPPER, NLS_UPPER

...where LOWER(clobCol1) = LOWER(clobCol2)

Yes

Yes

Character Functions

LPAD, RPAD

select RPAD(clobCol, 20, ' La') from...

Yes

Yes

Character Functions

TRIM, LTRIM, RTRIM

...where RTRIM(LTRIM(clobCol,'ab'), 'xy') = 'cd'

Yes

Yes

Character Functions

REPLACE

select REPLACE(clobCol, 'orig','new') from...

Yes

Yes

Character Functions

SOUNDEX

...where SOUNDEX(clobCOl) = SOUNDEX('SMYTHE')

CNV

CNV

Character Functions

SUBSTR

...where substr(clobCol, 1,4) = 'THIS'

Yes

Yes

Character Functions

TRANSLATE

select TRANSLATE(clobCol, '123abc','NC') from...

CNV

CNV

Character Functions

ASCII

select ASCII(clobCol) from...

CNV

CNV

Character Functions

INSTR

...where instr(clobCol, 'book') = 11

Yes

Yes

Character Functions

LENGTH

...where length(clobCol) != 7;

Yes

Yes

Character Functions

NLSSORT

...where NLSSORT (clobCol,'NLS_SORT = German') > NLSSORT ('S','NLS_SORT = German')

CNV

CNV

Character Functions

INSTRB, SUBSTRB, LENGTHB

These functions are supported only for CLOBs that use single-byte character sets. (LENGTHB is supported for BLOBs as well as CLOBs.)

Yes

Yes

Character Functions - Regular Expressions

REGEXP_LIKE

This function searches a character column for a pattern. Use this function in the WHERE clause of a query to return rows matching the regular expression you specify.
See the Oracle Database SQL Reference for syntax details on SQL functions for regular expressions. See the Oracle Database Application Developer's Guide - Fundamentals for information on using regular expressions with the database.

Yes

Yes

Character Functions - Regular Expressions

REGEXP_REPLACE

This function searches for a pattern in a character column and replaces each occurrence of that pattern with the pattern you specify.

Yes

Yes

Character Functions - Regular Expressions

REGEXP_INSTR

This function searches a string for a given occurrence of a regular expression pattern. You specify which occurrence you want to find and the start position to search from. This function returns an integer indicating the position in the string where the match is found.

Yes

Yes

Character Functions - Regular Expressions

REGEXP_SUBSTR

This function returns the actual substring matching the regular expression pattern you specify.

Yes

Yes

Conversion

CHARTOROWID

CHARTOROWID(clobCol)

CNV

CNV

Conversion

COMPOSE

COMPOSE('string')

Returns a Unicode string given a string in the datatype CHAR, VARCHAR2,CLOB, NCHAR, NVARCHAR2, NCLOB. An o code point qualified by an umlaut code point will be returned as the o-umlaut code point.

CNV

CNV

Conversion

DECOMPOSE

DECOMPOSE('str' [CANONICAL | COMPATIBILITY] )

Valid for Unicode character arguments. Returns a Unicode string after decomposition in the same character set as the input. o-umlaut code point will be returned as the o code point followed by the umlaut code point.

CNV

CNV

Conversion

HEXTORAW

HEXTORAW(CLOB)

No

CNV

Conversion

CONVERT

select CONVERT(clobCol,'WE8DEC','WE8HP') from...

Yes

CNV

Conversion

TO_DATE

TO_DATE(clobCol)

CNV

CNV

Conversion

TO_NUMBER

TO_NUMBER(clobCol)

CNV

CNV

Conversion

TO_TIMESTAMP

TO_TIMESTAMP(clobCol)

No

CNV

Conversion

TO_MULTI_BYTE
TO_SINGLE_BYTE

TO_MULTI_BYTE(clobCol)

TO_SINGLE_BYTE(clobCol)

CNV

CNV

Conversion

TO_CHAR

TO_CHAR(clobCol)

Yes

Yes

Conversion

TO_NCHAR

TO_NCHAR(clobCol)

Yes

Yes

Conversion

TO_LOB

INSERT INTO... SELECT TO_LOB(longCol)...

Note that TO_LOB can only be used to create or insert into a table with LOB columns as SELECT FROM a table with a LONG column.

N/A

N/A

Conversion

TO_CLOB

TO_CLOB(varchar2Col)

Yes

Yes

Conversion

TO_NCLOB

TO_NCLOB(varchar2Clob)

Yes

Yes

Aggregate Functions

COUNT

select count(clobCol) from...

No

N/A

Aggregate Functions

MAX, MIN

select MAX(clobCol) from...

No

N/A

Aggregate Functions

GROUPING

select grouping(clobCol) from... group by cube (clobCol);

No

N/A

Other Functions

GREATEST, LEAST

select GREATEST (clobCol1, clobCol2) from...

No

CNV

Other Functions

DECODE

select DECODE(clobCol, condition1, value1, defaultValue) from...

CNV

CNV

Other Functions

NVL

select NVL(clobCol,'NULL') from...

Yes

Yes

Other Functions

DUMP

select DUMP(clobCol) from...

No

N/A

Other Functions

VSIZE

select VSIZE(clobCol) from...

No

N/A

Unicode

INSTR2, SUBSTR2, LENGTH2, LIKE2

These functions use UCS2 code point semantics.

No

CNV

Unicode

INSTR4, SUBSTR4, LENGTH4, LIKE4

These functions use UCS4 code point semantics.

No

CNV

Unicode

INSTRC, SUBSTRC, LENGTHC, LIKEC

These functions use complete character semantics.

No

CNV

UNICODE Support

Variations on the INSTR, SUBSTR, LENGTH, and LIKE functions are provided for Unicode support. (These variations are indicated as "Unicode" in the "Category" column of Table 9-1.)

See Also:

- Oracle Database PL/SQL Packages and Types Reference

- Oracle Database Application Developer's Guide - Fundamentals

- Oracle Database SQL Reference

- Oracle Database Globalization Support Guide

for a detailed description on the usage of UNICODE functions.

Codepoint Semantics

Codepoint semantics of the INSTR, SUBSTR, LENGTH, and LIKE functions, described in Table 9-1, differ depending on the datatype of the argument passed to the function. These functions use different codepoint semantics depending on whether the argument is a VARCHAR2 or a CLOB type as follows:

- When the argument is a CLOB, UCS2 codepoint semantics are used for all character sets.

- When the argument is a character type, such as VARCHAR2, the default codepoint semantics are used for the given character set:

- UCS2 codepoint semantics are used for AL16UTF16 and UTF8 character sets.

- UCS4 codepoint semantics are used for all other character sets, such as AL32UTF8.

- If you are storing character data in a CLOB or NCLOB, then note that the amount and offset parameters for any APIs that read or write data to the CLOB or NCLOB are specified in UCS2 codepoints. In some character sets, a full character consists one or more UCS2 codepoints called a surrogate pair. In this scenario, you must ensure that the amount or offset you specify does not cut into a full character. This avoids reading or writing a partial character.

- Starting from 10g, Oracle Database helps to detect half surrogate pair on read/write boundaries in such scenarios. In the case of read, the offset and amount will be adjusted accordingly to avoid returning a half character, in which case the amount returned could be less than what is asked for. In the case of write, an error is raised to prevent from corrupting the existing data caused by overwriting a partial character in the destination CLOB or NCLOB.

Return Values for SQL Semantics on LOBs

The return type of a function or operator that takes a LOB or VARCHAR2 is the same as the datatype of the argument passed to the function or operator.

Functions that take more than one argument, such as CONCAT, return a LOB datatype if one or more arguments is a LOB. For example, CONCAT(CLOB, VARCHAR2) returns a CLOB.

See Also:

Oracle Database SQL Reference for details on the CONCAT function and the concatenation operator (||).

A LOB instance is always accessed and manipulated through a LOB locator. This is also true for return values: SQL functions and operators return a LOB locator when the return value is a LOB instance.

Any LOB instance returned by a SQL function is a temporary LOB instance. LOB instances in tables (persistent LOBs) are not modified by SQL functions, even when the function is used in the SELECT list of a query.

LENGTH Return Value for LOBs

The return value of the LENGTH function differs depending on whether the argument passed is a LOB or a character string:

- If the input is a character string of length zero, then LENGTH returns NULL.

- For a CLOB of length zero, or an empty locator such as that returned by EMPTY_CLOB(), the LENGTH and DBMS_LOB.GETLENGTH functions return FALSE.

Implicit Conversion of LOB Datatypes in SQL

Some LOB datatypes support implicit conversion and can be used in operations such as cross-type assignment and parameter passing. These conversions are processed at the SQL layer and can be performed in all client interfaces that use LOB types.

Implicit Conversion Between CLOB and NCLOB Datatypes in SQL

The database enables you to perform operations such as cross-type assignment and cross-type parameter passing between CLOB and NCLOB datatypes. The database performs implicit conversions between these types when necessary to preserve properties such as character set formatting.

Note that, when implicit conversions occur, each character in the source LOB is changed to the character set of the destination LOB, if needed. In this situation, some degradation of performance may occur if the data size is large. When the character set of the destination and the source are the same, there is no degradation of performance.

After an implicit conversion between CLOB and NCLOB types, the destination LOB is implicitly created as a temporary LOB. This new temporary LOB is independent from the source LOB. If the implicit conversion occurs as part of a define operation in a SELECT statement, then any modifications to the destination LOB do not affect the persistent LOB in the table that the LOB was selected from as shown in the following example:

SQL> -- check lob length before update
SQL> select dbms_lob.getlength(ad_sourcetext) from Print_media
2       where product_id=3106 and ad_id = 13001;

DBMS_LOB.GETLENGTH(AD_SOURCETEXT)
---------------------------------
205

SQL>
SQL> declare
2   clob1 clob;
3   amt number:=10;
4  BEGIN
5    -- select a clob column into a clob, no implicit convesion
6    SELECT ad_sourcetext INTO clob1 FROM Print_media
7      WHERE product_id=3106 and ad_id=13001 FOR UPDATE;
8
9    dbms_lob.trim(clob1, amt); -- Trim the selected lob to 10 bytes
10  END;
11  /

PL/SQL procedure successfully completed.

SQL> -- Modification is performed on clob1 which points to the
SQL> -- clob column in the table
SQL> select dbms_lob.getlength(ad_sourcetext) from Print_media
2       where product_id=3106 and ad_id = 13001;

DBMS_LOB.GETLENGTH(AD_SOURCETEXT)
---------------------------------
10

SQL>
SQL> rollback;

Rollback complete.

SQL> -- check lob length before update
SQL> select dbms_lob.getlength(ad_sourcetext) from Print_media
2       where product_id=3106 and ad_id = 13001;

DBMS_LOB.GETLENGTH(AD_SOURCETEXT)
---------------------------------
205

SQL>
SQL> declare
2   nclob1 nclob;
3   amt number:=10;
4  BEGIN
5
6    -- select a clob column into a nclob, implicit convesion occurs
7    SELECT ad_sourcetext INTO nclob1 FROM Print_media
8      WHERE product_id=3106 and ad_id=13001 FOR UPDATE;
9
10    dbms_lob.trim(nclob1, amt); -- Trim the selected lob to 10 bytes
11  END;
12  /

PL/SQL procedure successfully completed.

SQL> -- Modification to nclob1 does not affect the clob in the table,
SQL> -- because nclob1 is a independent temporary LOB

SQL> select dbms_lob.getlength(ad_sourcetext) from Print_media
2       where product_id=3106 and ad_id = 13001;

DBMS_LOB.GETLENGTH(AD_SOURCETEXT)
---------------------------------
205

See Also:

- "Implicit Conversions Between CLOB and VARCHAR2" for information on PL/SQL semantics support for implicit conversions between CLOB and VARCHAR2 types.

- "Implicit Character Set Conversions with LOBs" for more information on implicit character set conversions when loading LOBs from BILEs.

- Oracle Database SQL Reference for details on implicit conversions supported for all datatypes.

Unsupported Use of LOBs in SQL

Table 9-2 lists SQL operations that are not supported on LOB columns.

Table 9-2 Unsupported usage of LOBs in SQL

SQL Operations Not Supported

Example of unsupported usage

SELECT DISTINCT

SELECT DISTINCT clobCol from...

SELECT clause
ORDER BY

SELECT... ORDER BY clobCol

SELECT clause
GROUP BY

SELECT avg(num) FROM...

GROUP BY clobCol

UNION, INTERSECT, MINUS
(Note that UNION ALL works for LOBs.)

SELECT clobCol1 from tab1 UNION SELECT clobCol2 from tab2;

Join queries

SELECT... FROM... WHERE tab1.clobCol = tab2.clobCol

Index columns

CREATE INDEX clobIndx ON tab(clobCol)...

VARCHAR2 and RAW Semantics for LOBs

The following semantics, used with VARCHAR2 and RAW datatypes, also apply to LOBs:

- Defining a CHAR buffer on a CLOB

You can define a VARCHAR2 for a CLOB and RAW for a BLOB column. You can also define CLOB and BLOB types for VARCHAR2 and RAW columns.

- Selecting a CLOB column into a CHAR buffer or VARCHAR2

If a CLOB column is selected into a VARCHAR2 variable, then data stored in the CLOB column is retrieved and put into the CHAR buffer. If the buffer is not large enough to contain all the CLOB data, then a truncation error is thrown and no data is written to the buffer. After successful completion of the SELECT operation, the VARCHAR2 variable holds as a regular character buffer.

In contrast, when a CLOB column is selected into a local CLOB variable, the CLOB locator is fetched.

- Selecting a BLOB column into a RAW

When a BLOB column is selected into a RAW variable, the BLOB data is copied into the RAW buffer. If the size of the BLOB exceeds the size of the buffer, then a truncation error is thrown and no data is written to the buffer.

LOBs Returned from SQL Functions

When a LOB is returned from a SQL function, the result returned is a temporary LOB. Your application should view the temporary LOB as local storage for the data returned from the SELECT operation as follows:

- In PL/SQL, the temporary LOB has the same lifetime (duration) as other local PL/SQL program variables. It can be passed to subsequent SQL or PL/SQL VARCHAR2 functions or queries as a PL/SQL local variable. The temporary LOB will go out of scope at the end of the program block at which time, the LOB is freed. These are the same semantics as those for PL/SQL VARCHAR2 variables. At any time, nonetheless, you can use a DBMS_LOB.FREETEMPORARY call to release the resources taken by the local temporary LOBs.

- In OCI, the temporary LOBs returned from SQL queries are always in 'session' duration, unless a user-defined duration is present, in which case, the temporary LOBs will be in the user-defined duration.

Caution:

Ensure that your temporary tablespace is large enough to store all temporary LOB results returned from queries in your program(s).

The following example illustrates selecting out a CLOB column into a VARCHAR2 and returning the result as a CHAR buffer of declared size:

DECLARE
vc1 VARCHAR2(32000);
lb1 CLOB;
lb2 CLOB;
BEGIN
SELECT clobCol1 INTO vc1 FROM tab WHERE colID=1;
-- lb1 is a temporary LOB
SELECT clobCol2 || clobCol3 INTO lb1 FROM tab WHERE colID=2;

lb2 := vc1|| lb1;
-- lb2 is a still temporary LOB, so the persistent data in the database
-- is not modified. An update is necessary to modify the table data.
UPDATE tab SET clobCol1 = lb2 WHERE colID = 1;

DBMS_LOB.FREETEMPORARY(lb2); -- Free up the space taken by lb2

<... some more queries ...>

END; -- at the end of the block, lb1 is automatically freed

IS NULL and IS [NOT] NULL Usage with VARCHAR2s and CLOBs

You can use the IS NULL and IS [NOT] NULL operators with LOB columns. When used with LOBs, these operators determine whether a LOB locator is stored in the row.

Note:

In the SQL 92 standard, a character string of length zero is distinct from a NULL string. The return value of IS NULL differs when you pass a LOB compared to a VARCHAR2:

- When you pass an initialized LOB of length zero to the IS NULL function, zero (FALSE) is returned. These semantics are compliant with the SQL standard.

- When you pass a VARCHAR2 of length zero to the IS NULL function, TRUE is returned.

WHERE Clause Usage with LOBs

SQL functions with LOBs as arguments, except functions that compare LOB values, are allowed in predicates of the WHERE clause. For example, the LENGTH function can be included in the predicate of the WHERE clause:

create table t (n number, c clob);
insert into t values (1, 'abc');

select * from t where c is not null;
select * from t where length(c) > 0;
select * from t where c like '%a%';
select * from t where substr(c, 1, 2) like '%b%';
select * from t where instr(c, 'b') = 2;

10 PL/SQL Semantics for LOBs

This chapter contains these topics:

- PL/SQL Statements and Variables

- Implicit Conversions Between CLOB and VARCHAR2

- Explicit Conversion Functions

- PL/SQL CLOB Comparison Rules

PL/SQL Statements and Variables

In PL/SQL, a number of semantic changes have been made as described in the previous paragraphs.

Note:

The following discussions, concerning CLOBs and VARCHAR2s, also apply to BLOBs and RAWs, unless otherwise noted. In the text, BLOB and RAW are not explicitly mentioned.

PL/SQL semantics support is described in the following sections:

- Implicit Conversions Between CLOB and VARCHAR2

- Explicit Conversion Functions

- VARCHAR2 and CLOB in PL/SQL Built-In Functions

- PL/SQL CLOB Comparison Rules

Implicit Conversions Between CLOB and VARCHAR2

Implicit conversions from CLOB to VARCHAR2 and from VARCHAR2 to CLOB datatypes are allowed in PL/SQL. These conversions enable you to perform the following operations in your application:

- CLOB columns can be selected into VARCHAR2 PL/SQL variables

- VARCHAR2 columns can be selected into CLOB variables

- Assignment and parameter passing between CLOBs and VARCHAR2s

Accessing a CLOB as a VARCHAR2 in PL/SQL

The following example illustrates the way CLOB data is accessed when the CLOBs are treated as VARCHAR2s:

declare
myStoryBuf VARCHAR2(4001);
BEGIN
SELECT ad_sourcetext INTO myStoryBuf FROM print_media WHERE ad_id = 12001;
-- Display Story by printing myStoryBuf directly
END;
/

Assigning a CLOB to a VARCHAR2 in PL/SQL

declare
myLOB CLOB;
BEGIN
SELECT 'ABCDE' INTO myLOB FROM print_media WHERE ad_id = 11001;
-- myLOB is a temporary LOB.
-- Use myLOB as a lob locator
DBMS_OUTPUT.PUT_LINE('Is temp? '||DBMS_LOB.ISTEMPORARY(myLOB));
END;
/

Explicit Conversion Functions

In SQL and PL/SQL, the following explicit conversion functions convert other data types to and from CLOB, NCLOB, and BLOB as part of the LONG-to-LOB migration:

- TO_CLOB(): Converting from VARCHAR2, NVARCHAR2, or NCLOB to a CLOB

- TO_NCLOB(): Converting from VARCHAR2, NVARCHAR2, or CLOB to an NCLOB

- TO_BLOB(): Converting from RAW to a BLOB

- TO_CHAR() converts a CLOB to a CHAR type. When you use this function to convert a character LOB into the database character set, if the LOB value to be converted is larger than the target type, then the database returns an error. Implicit conversions also raise an error if the LOB data does not fit.

- TO_NCHAR() converts an NCLOB to an NCHAR type. When you use this function to convert a character LOB into the national character set, if the LOB value to be converted is larger than the target type, then the database returns an error. Implicit conversions also raise an error if the LOB data does not fit.

- CAST does not directly support any of the LOB datatypes. When you use CAST to convert a CLOB value into a character datatype, an NCLOB value into a national character datatype, or a BLOB value into a RAW datatype, the database implicitly converts the LOB value to character or raw data and then explicitly casts the resulting value into the target datatype. If the resulting value is larger than the target type, then the database returns an error.

Other explicit conversion functions are not supported, such as, TO_NUMBER(), see Table 9-1, "SQL VARCHAR2 Functions and Operators on LOBs". Conversion function details are explained in Chapter 11, "Migrating Columns from LONGs to LOBs".

VARCHAR2 and CLOB in PL/SQL Built-In Functions

CLOB and VARCHAR2 are still two distinct types. But depending on the usage, a CLOB can be passed to SQL and PL/SQL VARCHAR2 built-in functions, used exactly like a VARCHAR2. Or the variable can be passed into DBMS_LOB APIs, acting like a LOB locator. Please see the following combined example,"CLOB Variables in PL/SQL".

PL/SQL VARCHAR2 functions and operators can take CLOBs as arguments or operands.

When the size of a VARCHAR2 variable is not large enough to contain the result from a function that returns a CLOB, or a SELECT on a CLOB column, an error should be raised and no operation will be performed. This is consistent with VARCHAR2 semantics.

CLOB Variables in PL/SQL

1 declare
2   myStory CLOB;
3   revisedStory CLOB;
4   myGist VARCHAR2(100);
5   revisedGist VARCHAR2(100);
6 BEGIN
7  -- select a CLOB column into a CLOB variable
8  SELECT Story INTO myStory FROM print_media WHERE product_id=10;
9  -- perform VARCHAR2 operations on a CLOB variable
10 revisedStory := UPPER(SUBSTR(myStory, 100, 1));
11 -- revisedStory is a temporary LOB
12 -- Concat a VARCHAR2 at the end of a CLOB
13 revisedStory := revisedStory || myGist;
14 -- The following statement will raise an error because myStory is
15 -- longer than 100 bytes
16 myGist := myStory;
17 END;

Please note that in line 10 of "CLOB Variables in PL/SQL", a temporary CLOB is implicitly created and is pointed to by the revisedStory CLOB locator. In the current interface the line can be expanded as:

buffer VARCHAR2(32000)
DBMS_LOB.CREATETEMPORARY(revisedStory);
buffer := UPPER(DBMS_LOB.SUBSTR(myStory,100,1));
DBMS_LOB.WRITE(revisedStory,length(buffer),1, buffer);

In line 13, myGist is appended to the end of the temporary LOB, which has the same effect of:

DBMS_LOB.WRITEAPPEND(revisedStory, myGist, length(myGist));

In some occasions, implicitly created temporary LOBs in PL/SQL statements can change the representation of LOB locators previously defined. Consider the next example.

Change in Locator-Data Linkage

1 declare
2 myStory CLOB;
3 amt number:=100;
4 buffer VARCHAR2(100):='some data';
5 BEGIN
6 -- select a CLOB column into a CLOB variable
7 SELECT Story INTO myStory FROM print_media WHERE product_id=10;
8 DBMS_LOB.WRITE(myStory, amt, 1, buf);
9 -- write to the persistent LOB in the table
10
11 myStory:= UPPER(SUBSTR(myStory, 100, 1));
12 -- perform VARCHAR2 operations on a CLOB variable, temporary LOB created.
13 -- Changes will not be reflected in the database table from this point on.
14
15 update print_media set Story = myStory WHERE product_id = 10;
16 -- an update is necessary to synchronize the data in the table.
17 END;

After line 7, myStory represents a persistent LOB in print_media.

The DBMS_LOB.WRITE call in line 8 directly writes the data to the table.

No UPDATE statement is necessary. Subsequently in line 11, a temporary LOB is created and assigned to myStory because myStory is now used like a local VARCHAR2 variable. The LOB locator myStory now points to the newly-created temporary LOB.

Therefore, modifications to myStory will no longer be reflected in the database. To propagate the changes to the database table, an UPDATE statement becomes necessary now. Note again that for the previous persistent LOB, the UPDATE is not required.

Temporary LOBs created in a program block as a result of a SELECT or an assignment are freed automatically at the end of the PL/SQL block/function/procedure. You can choose to free the temporary LOBs to reclaim system resources and temporary tablespace by calling DBMS_LOB.FREETEMPORARY on the CLOB variable.

Freeing Temporary LOBs Automatically and Manually

declare
Story1 CLOB;
Story2 CLOB;
StoryCombined CLOB;
StoryLower CLOB;
BEGIN
SELECT Story INTO Story1 FROM print_media WHERE product_ID = 1;
SELECT Story INTO Story2 FROM print_media WHERE product_ID = 2;
StoryCombined := Story1 || Story2; -- StoryCombined is a temporary LOB
-- Free the StoryCombined manually to free up space taken
DBMS_LOB.FREETEMPORARY(StoryCombined);
StoryLower := LOWER(Story1) || LOWER(Story2);
END; -- At the end of block, StoryLower is freed.

PL/SQL CLOB Comparison Rules

Like VARCHAR2s, when a CLOB is compared with another CLOB or compared with a VARCHAR2, a set of rules determines the comparison. The rules are usually called a "collating sequence". In Oracle, CHARs and VARCHAR2s have slightly different sequences due to the blank padding of CHARs.

CLOBs Follow the VARCHAR2 Collating Sequence

As a rule, CLOBs follow the same collating sequence as VARCHAR2s. That is, when a CLOB is compared, the result is consistent with if the CLOB data content is retrieved into a VARCHAR2 buffer and the VARCHAR2 is compared. The rule applies to all cases including comparisons between CLOB and CLOB, CLOB and VARCHAR2, and CLOB and CHAR.

Note:

When a CLOB is compared with a CHAR string, it is always the character data of the CLOB being compared with the string. Likewise, when two CLOBs are compared, the data content of the two CLOBs are compared, not their LOB locators.

It makes no sense to compare CLOBs with non-character data, or with BLOBs. An error is returned in these cases.

11 Migrating Columns from LONGs to LOBs

This chapter describes techniques for migrating tables that use LONG datatypes to LOB datatypes. This chapter contains these topics:

- Benefits of Migrating LONG Columns to LOB Columns

- Preconditions for Migrating LONG Columns to LOB Columns

- Using utldtree.sql to Determine Where Your Application Needs Change

- Converting Tables from LONG to LOB Datatypes

- Migrating Applications from LONGs to LOBs

See Also:

The following chapters in this book describe support for LOB datatypes in various programming environments:

- Chapter 9, "SQL Semantics and LOBs"

- Chapter 10, "PL/SQL Semantics for LOBs"

- Chapter 13, "Data Interface for Persistent LOBs"

Benefits of Migrating LONG Columns to LOB Columns

There are many benefits to migrating table columns from LONG datatypes to LOB datatypes.

Note:

You can use the techniques described in this chapter to do either of the following:

- Convert columns of type LONG to either CLOB or NCLOB columns

- Convert columns of type LONG RAW to BLOB type columns

Unless otherwise noted, discussions in this chapter regarding "LONG to LOB" conversions apply to both of these datatype conversions.

The following list compares the semantics of LONG and LOB datatypes in various application development scenarios:

- The number of LONG type columns is limited. Any given table can have a maximum of only one LONG type column. The number of LOB type columns in a table is not limited.

- You can use the data interface for LOBs to enable replication of tables that contain LONG or LONG RAW columns. Replication is allowed on LOB columns, but is not supported for LONG and LONG RAW columns. The database omits columns containing LONG and LONG RAW datatypes from replicated tables.

If a table is replicated or has materialized views, and its LONG column is changed to LOB, then you may have to manually fix the replicas.

Caution:

Converting LOB datatypes back to LONG datatypes is not supported. Ensure that you do not need to maintain any column as a LONG datatype before converting the column to a LOB type.

Preconditions for Migrating LONG Columns to LOB Columns

This section describes preconditions that must be met before converting a LONG column to a LOB column.

See Also:

"Migrating Applications from LONGs to LOBs" before converting your table to determine whether any limitations on LOB columns will prevent you from converting to LOBs.

Dropping a Domain Index on a LONG Column Before Converting to a LOB

Any domain index on a LONG column must be dropped before converting the LONG column to LOB column. See "Indexes on Columns Converted from LONG to LOB Datatypes" for more information.

Preventing Generation of Redo Space on Tables Converted to LOB Datatypes

Generation of redo space can cause performance problems during the process of converting LONG columns. Redo changes for the table are logged during the conversion process only if the table has LOGGING on.

Redo changes for the column being converted from LONG to LOB are logged only if the storage characteristics of the LOB column indicate LOGGING. The logging setting (LOGGING or NOLOGGING) for the LOB column is inherited from the tablespace in which the LOB is created.

To prevent generation of redo space during migration, do the following before migrating your table (syntax is in BNF):

1. ALTER TABLE Long_tab NOLOGGING;

2. ALTER TABLE Long_tab MODIFY (long_col CLOB [DEFAULT <default_val>]) LOB (long_col) STORE AS (NOCACHE NOLOGGING);
Note that you must also specify NOCACHE when you specify NOLOGGING in the STORE AS clause.

3. ALTER TABLE Long_tab MODIFY LOB (long_col) (CACHE);

4. ALTER TABLE Long_tab LOGGING;

5. Make a backup of the tablespaces containing the table and the LOB column.

Using utldtree.sql to Determine Where Your Application Needs Change

You can use the utility, rdbms/admin/utldtree.sql, to determine which parts of your application require rewriting when you migrate your table from LONG to LOB column types. This utility enables you to recursively see all objects that are dependent on a given object. For example, you can see all objects which depend on a table with a LONG column. You will only see objects for which you have permission.

Instructions on how to use utldtree.sql are documented in the file itself. Also, utldtree.sql is only needed for PL/SQL. For SQL and OCI you do not need to change your applications.

Converting Tables from LONG to LOB Datatypes

This section describes the following techniques for migrating existing tables from LONG to LOB datatypes:

- Using ALTER TABLE to Convert LONG Columns to LOB Columns

- Copying a LONG to a LOB Column Using the TO_LOB Operator

- Online Redefinition of Tables with LONG Columns where high availability is critical

Using ALTER TABLE to Convert LONG Columns to LOB Columns

You can use the ALTER TABLE statement in SQL to convert a LONG column to a LOB column. To do so, use the following syntax:

ALTER TABLE [<schema>.]<table_name>
MODIFY ( <long_column_name> { CLOB | BLOB | NCLOB }
[DEFAULT <default_value>]) [LOB_storage_clause];

For example, if you had a table that was created as follows:

CREATE TABLE Long_tab (id NUMBER, long_col LONG);

then you can change the column long_col in table Long_tab to datatype CLOB using following ALTER TABLE statement:

ALTER TABLE Long_tab MODIFY ( long_col CLOB );

Note:

The ALTER TABLE statement copies the contents of the table into a new space, and frees the old space at the end of the operation. This temporarily doubles the space requirements.

Note that when using the ALTER TABLE statement to convert a LONG column to a LOB column, only the following options are allowed:

- DEFAULT which enables you to specify a default value for the LOB column.

- The LOB_storage_clause, which enables you to specify the LOB storage characteristics for the converted column, can be specified in the MODIFY clause.

Other ALTER TABLE options are not allowed when converting a LONG column to a LOB type column.

Migration Issues

General issues concerning migration include the following:

- All constraints of your previous LONG columns are maintained for the new LOB columns. The only constraint allowed on LONG columns are NULL and NOT NULL. To alter the constraints for these columns, or alter any other columns or properties of this table, you have to do so in a subsequent ALTER TABLE statement.

- If you do not specify a default value, then the default value for the LONG column becomes the default value of the LOB column.

- Most of the existing triggers on your table are still usable, however UPDATE OF triggers can cause issues. See "Migrating Applications from LONGs to LOBs" for more details.

Copying a LONG to a LOB Column Using the TO_LOB Operator

If you do not want to use ALTER TABLE, as described earlier in this section, then you can use the TO_LOB operator on a LONG column to copy it to a LOB column. You can use the CREATE TABLE AS SELECT statement or the INSERT AS SELECT statement with the TO_LOB operator to copy data from a LONG column to a CLOB or NCLOB column, or from a LONG RAW column to a BLOB column. For example, if you have a table with a LONG column that was created as follows:

CREATE TABLE Long_tab (id NUMBER, long_col LONG);

then you can do the following to copy the column to a LOB column:

CREATE TABLE Lob_tab (id NUMBER, clob_col CLOB);
INSERT INTO Lob_tab SELECT id, TO_LOB(long_col) FROM long_tab;
COMMIT;

If the INSERT returns an error (because of lack of undo space), then you can incrementally migrate LONG data to the LOB column using the WHERE clause. After you ensure that the data is accurately copied, you can drop the original table and create a view or synonym for the new table using one of the following sequences:

DROP TABLE Long_tab;
CREATE VIEW Long_tab (id, long_col) AS SELECT * from Lob_tab;

or

DROP TABLE Long_tab;
CREATE SYNONYM Long_tab FOR Lob_tab;

This series of operations is equivalent to changing the datatype of the column Long_col of table Long_tab from LONG to CLOB. With this technique, you have to re-create any constraints, triggers, grants and indexes on the new table.

Use of the TO_LOB operator is subject to the following limitations:

- You can use TO_LOB to copy data to a LOB column, but not to a LOB attribute of an object type.

- You cannot use TO_LOB with a remote table. For example, the following statements will not work:

INSERT INTO tb1@dblink (lob_col) SELECT TO_LOB(long_col) FROM tb2;
INSERT INTO tb1 (lob_col) SELECT TO_LOB(long_col) FROM tb2@dblink;
CREATE TABLE tb1 AS SELECT TO_LOB(long_col) FROM tb2@dblink;

- The TO_LOB operator cannot be used in the CREATE TABLE AS SELECT statement to convert a LONG or LONG RAW column to a LOB column when creating an index organized table.

To work around this limitation, create the index organized table, and then do an INSERT AS SELECT of the LONG or LONG RAW column using the TO_LOB operator.

- You cannot use TO_LOB inside any PL/SQL block.

Online Redefinition of Tables with LONG Columns

Tables with LONG and LONG RAW columns can be migrated using online table redefinition. This technique is suitable for migrating LONG columns in database tables where high availability is critical.

To use this technique, you must convert LONG columns to LOB types during the redefinition process as follows:

- Any LONG column must be converted to a CLOB or NCLOB column.

- Any LONG RAW column must be converted to a BLOB column.

This conversion is performed using the TO_LOB() operator in the column mapping of the DBMS_REDEFINITION.START_REDEF_TABLE() procedure.

Note:

You cannot perform online redefinition of tables with LONG or LONG RAW columns unless you convert the columns to LOB types as described in this section.

General tasks involved in the online redefinition process are given in the following list. Issues specific to converting LONG and LONG RAW columns are called out. See the related documentation referenced at the end of this section for additional details on the online redefinition process that are not described here.

- Create an empty interim table. This table will hold the migrated data when the redefinition process is done. In the interim table:

- Define a CLOB or NCLOB column for each LONG column in the original table that you are migrating.

- Define a BLOB column for each LONG RAW column in the original table that you are migrating.

- Start the redefinition process. To do so, call DBMS_REDEFINITION.START_REDEF_TABLE and pass the column mapping using the TO_LOB operator as follows:

DBMS_REDEFINITION.START_REDEF_TABLE(
'schema_name',
'original_table',
'interim_table',
'TO_LOB(long_col_name) lob_col_name',
'options_flag',
'orderby_cols');

where long_col_name is the name of the LONG or LONG RAW column that you are converting in the original table and lob_col_name is the name of the LOB column in the interim table. This LOB column will hold the converted data.

- Call the DBMS_REDEFINITION.COPY_TABLE_DEPENDENTS procedure as described in the related documentation.

- Call the DBMS_REDEFINITION.FINISH_REDEF_TABLE procedure as described in the related documentation.

Parallel Online Redefinition

On a system with sufficient resources for parallel execution, redefinition of a LONG column to a LOB column can be executed in parallel under the following conditions:

In the case where the destination table is non-partitioned:

- The segment used to store the LOB column in the destination table belongs to a locally managed tablespace with Automatic Segment Space Management (ASSM) enabled, which is now the default.

- There is a simple mapping from one LONG column to one LOB column, and the destination table has only one LOB column.

In the case where the destination table is partitioned, the normal methods for parallel execution for partitioning apply. When the destination table is partitioned, then online redefinition is executed in parallel.

Example of Online Redefinition

The following example demonstrates online redefinition with LOB columns.

REM Grant privleges required for online redefinition.
GRANT execute ON DBMS_REDEFINITION TO pm;
GRANT ALTER ANY TABLE TO pm;
GRANT DROP ANY TABLE TO pm;
GRANT LOCK ANY TABLE TO pm;
GRANT CREATE ANY TABLE TO pm;
GRANT SELECT ANY TABLE TO pm;

REM Privileges required to perform cloning of dependent objects.
GRANT CREATE ANY TRIGGER TO pm;
GRANT CREATE ANY INDEX TO pm;

connect pm/pm

drop table cust;
create table cust(c_id   number primary key,
c_zip  number,
c_name varchar(30) default null,
c_long long
);
insert into cust values(1, 94065, 'hhh', 'ttt');

-- Creating Interim Table
-- There is no need to specify constraints because they are
-- copied over from the original table.
create table cust_int(c_id   number not null,
c_zip  number,
c_name varchar(30) default null,
c_long clob
);

declare
col_mapping varchar2(1000);
BEGIN
--  map all the columns in the interim table to the original table
col_mapping :=
'c_id             c_id  , '||
'c_zip            c_zip , '||
'c_name           c_name, '||
'to_lob(c_long)   c_long';

dbms_redefinition.start_redef_table('pm', 'cust', 'cust_int', col_mapping);
END;
/

declare
error_count pls_integer := 0;
BEGIN
dbms_redefinition.copy_table_dependents('pm', 'cust', 'cust_int',
1, true,true,true,false,
error_count);

dbms_output.put_line('errors := ' || to_char(error_count));
END;
/

exec  dbms_redefinition.finish_redef_table('pm', 'cust', 'cust_int');

-- Drop the interim table
drop table cust_int;

desc cust;

-- The following insert statement fails. This illustrates
-- that the primary key constraint on the c_id column is
-- preserved after migration.

insert into cust values(1, 94065, 'hhh', 'ttt');

select * from cust;

See Also:

The following related documentation provides additional details on the redefinition process described earlier in this section:

- Oracle Database Administrator's Guide gives detailed procedures and examples of redefining tables online.

- Oracle Database PL/SQL Packages and Types Reference includes information on syntax and other details on usage of procedures in the DBMS_REDEFINITION package.

Migrating Applications from LONGs to LOBs

This section discusses differences between LONG and LOB datatypes that may impact your application migration plans or require you to modify your application.

Most APIs that work with LONG datatypes in the PL/SQL and OCI environments are enhanced to also work with LOB datatypes. These APIs are collectively referred to as the data interface for persistent LOBs, or simply the data interface. Among other things, the data interface provides the following benefits:

- Changes needed are minimal in PL/SQL and OCI applications that use tables with columns converted from LONG to LOB datatypes.

- You can work with LOB datatypes in your application without having to deal with LOB locators.

See Also:

- Chapter 13, "Data Interface for Persistent LOBs" for details on PL/SQL and OCI APIs included in the data interface.

- Chapter 9, "SQL Semantics and LOBs" for details on SQL syntax supported for LOB datatypes.

- Chapter 10, "PL/SQL Semantics for LOBs" for details on PL/SQL syntax supported for LOB datatypes.

LOB Columns Are Not Allowed in Clustered Tables

LOB columns are not allowed in clustered tables, whereas LONGs are allowed. If a table is a part of a cluster, then any LONG or LONG RAW column cannot be changed to a LOB column.

LOB Columns Are Not Allowed in UPDATE OF Triggers

You cannot have LOB columns in the UPDATE OF list of an UPDATE OF trigger. LONG columns are allowed in such triggers. For example, the following create trigger statement is not valid:

create table t(lobcol CLOB);
create trigger trig before/after update of lobcol on t ...;

All other triggers work on LOB columns.

Indexes on Columns Converted from LONG to LOB Datatypes

Indexes on any column of the table being migrated must be manually rebuilt after converting any LONG column to a LOB column. This includes function-based indexes.

Any function-based index on a LONG column will be unusable during the conversion process and must be rebuilt after converting. Application code that uses function-based indexing should work without modification after converting.

Note that, any domain indexes on a LONG column must be dropped before converting the LONG column to LOB column. You can rebuild the domain index after converting.

To rebuild an index after converting, use the following steps:

1. Select the index from your original table as follows:

SELECT index_name FROM user_indexes WHERE table_name='LONG_TAB';

Note:

The table name must be capitalized in this query.

2. For the selected index, use the command:

ALTER INDEX <index> REBUILD

Empty LOBs Compared to NULL and Zero Length LONGs

A LOB column can hold an empty LOB. An empty LOB is a LOB locator that is fully initialized, but not populated with data. Because LONG datatypes do not use locators, the "empty" concept does not apply to LONG datatypes.

Both LOB column values and LONG column values, inserted with an initial value of NULL or an empty string literal, have a NULL value. Therefore, application code that uses NULL or zero-length values in a LONG column will function exactly the same after you convert the column to a LOB type column.

In contrast, a LOB initialized to empty has a non-NULL value as illustrated in the following example:

CREATE TABLE long_tab(id NUMBER, long_col LONG);
CREATE TABLE lob_tab(id NUMBER, lob_col CLOB);

INSERT INTO long_tab values(1, NULL);

REM     A zero length string inserts a NULL into the LONG column:
INSERT INTO long_tab values(1, '');

INSERT INTO lob_tab values(1, NULL);

REM     A zero length string inserts a NULL into the LOB column:
INSERT INTO lob_tab values(1, '');

REM     Inserting an empty LOB inserts a non-NULL value:
INSERT INTO lob_tab values(1, empty_clob());

DROP TABLE long_tab;
DROP TABLE lob_tab;

Overloading with Anchored Types

For applications using anchored types, some overloaded variables resolve to different targets during the conversion to LOBs. For example, given the procedure p overloaded with specifications 1 and 2:

procedure p(l long) is ...;       -- (specification 1)
procedure p(c clob) is ...;       -- (specification 2)

and the procedure call:

declare
var  longtab.longcol%type;
BEGIN
...
p(var);
...
END;

Prior to migrating from LONG to LOB columns, this call would resolve to specification 1. Once longtab is migrated to LOB columns this call will resolve to specification 2. Note that this would also be true if the parameter type in specification 1 were a CHAR, VARCHAR2, RAW, LONG RAW.

If you have migrated you tables from LONG columns to LOB columns, then you must manually examine your applications and determine whether overloaded procedures must be changed.

Some applications that included overloaded procedures with LOB arguments before migrating may still break. This includes applications that do not use LONG anchored types. For example, given the following specifications (1 and 2) and procedure call for procedure p:

procedure p(n number) is ...;       -- (1)
procedure p(c clob) is ...;         -- (2)

p('123');             -- procedure call

Before migrating, the only conversion allowed was CHAR to NUMBER, so specification 1 would be chosen. After migrating, both conversions are allowed, so the call is ambiguous and raises an overloading error.

Some Implicit Conversions Are Not Supported for LOB Datatypes

PL/SQL permits implicit conversion from NUMBER, DATE, ROW_ID, BINARY_INTEGER, and PLS_INTEGER datatypes to a LONG; however, implicit conversion from these datatypes to a LOB is not allowed.

If your application uses these implicit conversions, then you will have to explicitly convert these types using the TO_CHAR operator for character data or the TO_RAW operator for binary data. For example, if your application has an assignment operation such as:

number_var := long_var;  -- The RHS is a LOB variable after converting.

then you must modify your code as follows:

number_var := TO_CHAR(long_var);
-- Assuming that long_var is of type CLOB after conversion

The following conversions are not supported for LOB types:

- BLOB to VARCHAR2, CHAR, or LONG

- CLOB to RAW or LONG RAW

This applies to all operations where implicit conversion takes place. For example if you have a SELECT statement in your application as follows:

SELECT long_raw_column INTO my_varchar2 VARIABLE FROM my_table

and long_raw_column is a BLOB after converting your table, then the SELECT statement will produce an error. To make this conversion work, you must use the TO_RAW operator to explicitly convert the BLOB to a RAW as follows:

SELECT TO_RAW(long_raw_column) INTO my_varchar2 VARIABLE FROM my_table

The same holds for selecting a CLOB into a RAW variable, or for assignments of CLOB to RAW and BLOB to VARCHAR2.

Part IV

Using LOB APIs

This part provides details on using LOB APIs in supported environments. Examples of LOB API usage are given.

This part contains these chapters:

- Chapter 12, "Operations Specific to Persistent and Temporary LOBs"

- Chapter 13, "Data Interface for Persistent LOBs"

- Chapter 14, " LOB APIs for Basic Operations"

- Chapter 15, "LOB APIs for BFILE Operations"

12 Operations Specific to Persistent and Temporary LOBs

This chapter discusses LOB operations that differ between persistent and temporary LOB instances. This chapter contains these topics:

- Persistent LOB Operations

- Temporary LOB Operations

- Creating Persistent and Temporary LOBs in PL/SQL

See Also:

- Chapter 14, " LOB APIs for Basic Operations" gives details and examples of API usage for LOB APIs that can be used with either temporary or persistent LOBs.

- Chapter 15, "LOB APIs for BFILE Operations" gives details and examples for usage of LOB APIs that operate on BFILEs.

Persistent LOB Operations

This section describes operations that apply only to persistent LOBs.

Inserting a LOB into a Table

You can insert LOB instances into persistent LOB columns using any of the methods described in Chapter 8, "DDL and DML Statements with LOBs".

Selecting a LOB from a Table

You can select a persistent LOB from a table just as you would any other datatype. In the following example, persistent LOB instances of different types are selected into PL/SQL variables.

declare
blob1 BLOB;
blob2 BLOB;
clob1 CLOB;
nclob1 NCLOB;
BEGIN
SELECT ad_photo INTO blob1 FROM print_media WHERE Product_id = 2268
FOR UPDATE;
SELECT ad_photo INTO blob2 FROM print_media WHERE Product_id = 3106;

SELECT ad_sourcetext INTO clob1 FROM Print_media
WHERE product_id=3106 and ad_id=13001 FOR UPDATE;

SELECT ad_fltextn INTO nclob1 FROM Print_media
WHERE product_id=3060 and ad_id=11001 FOR UPDATE;

END;
/
show errors;

Temporary LOB Operations

This section describes operations that apply only to temporary LOB instances.

Creating and Freeing a Temporary LOB

To create a temporary LOB instance, you must declare a variable of the given LOB datatype and pass the variable to the CREATETEMPORARY API. The temporary LOB instance will exist in your application until it goes out of scope, your session terminates, or you explicitly free the instance. Freeing a temporary LOB instance is recommended to free system resources.

The following example demonstrates how to create and free a temporary LOB in the PL/SQL environment using the DBMS_LOB package.

declare
blob1 BLOB;
blob2 BLOB;
clob1 CLOB;
nclob1 NCLOB;
BEGIN
-- create temp LOBs
DBMS_LOB.CREATETEMPORARY(blob1,TRUE, DBMS_LOB.SESSION);
DBMS_LOB.CREATETEMPORARY(blob2,TRUE, DBMS_LOB.SESSION);
DBMS_LOB.CREATETEMPORARY(clob1,TRUE, DBMS_LOB.SESSION);
DBMS_LOB.CREATETEMPORARY(nclob1,TRUE, DBMS_LOB.SESSION);

-- fill with data
writeDataToLOB_proc(blob1);
writeDataToLOB_proc(blob2);

-- CHAR->LOB conversion
clob1 := 'abcde';
nclob1 := TO_NCLOB(clob1);

-- Other APIs
call_lob_apis(blob1, blob2, clob1, nclob1);

-- free temp LOBs
DBMS_LOB.FREETEMPORARY(blob1);
DBMS_LOB.FREETEMPORARY(blob2);
DBMS_LOB.FREETEMPORARY(clob1);
DBMS_LOB.FREETEMPORARY(nclob1);

END;
/
show errors;

Creating Persistent and Temporary LOBs in PL/SQL

The code example that follows illustrates how to create persistent and temporary LOBs in PL/SQL. This code is in the demonstration file:

$ORACLE_HOME/rdbms/demo/lobs/plsql/lobdemo.sql */

This demonstration file also calls procedures in separate PL/SQL files that illustrate usage of other LOB APIs. For a list of these files and links to more information about related LOB APIs, see "PL/SQL LOB Demonstration Files".

-----------------------------------------------------------------------------
-------------------------  Persistent LOB operations ------------------------
-----------------------------------------------------------------------------

declare
blob1 BLOB;
blob2 BLOB;
clob1 CLOB;
nclob1 NCLOB;
BEGIN
SELECT ad_photo INTO blob1 FROM print_media WHERE Product_id = 2268
FOR UPDATE;
SELECT ad_photo INTO blob2 FROM print_media WHERE Product_id = 3106;

SELECT ad_sourcetext INTO clob1 FROM Print_media
WHERE product_id=3106 and ad_id=13001 FOR UPDATE;

SELECT ad_fltextn INTO nclob1 FROM Print_media
WHERE product_id=3060 and ad_id=11001 FOR UPDATE;

call_lob_apis(blob1, blob2, clob1, nclob1);
rollback;
END;
/
show errors;

-----------------------------------------------------------------------------
-------------------------  Temporary LOB operations ------------------------
-----------------------------------------------------------------------------

declare
blob1 BLOB;
blob2 BLOB;
clob1 CLOB;
nclob1 NCLOB;
BEGIN
-- create temp LOBs
DBMS_LOB.CREATETEMPORARY(blob1,TRUE, DBMS_LOB.SESSION);
DBMS_LOB.CREATETEMPORARY(blob2,TRUE, DBMS_LOB.SESSION);
DBMS_LOB.CREATETEMPORARY(clob1,TRUE, DBMS_LOB.SESSION);
DBMS_LOB.CREATETEMPORARY(nclob1,TRUE, DBMS_LOB.SESSION);

-- fill with data
writeDataToLOB_proc(blob1);
writeDataToLOB_proc(blob2);

-- CHAR->LOB conversion
clob1 := 'abcde';
nclob1 := TO_NCLOB(clob1);

-- Other APIs
call_lob_apis(blob1, blob2, clob1, nclob1);

-- free temp LOBs
DBMS_LOB.FREETEMPORARY(blob1);
DBMS_LOB.FREETEMPORARY(blob2);
DBMS_LOB.FREETEMPORARY(clob1);
DBMS_LOB.FREETEMPORARY(nclob1);

END;
/
show errors;

13 Data Interface for Persistent LOBs

This chapter contains these topics:

- Overview of the Data Interface for Persistent LOBs

- Benefits of Using the Data Interface for Persistent LOBs

- Using the Data Interface for Persistent LOBs in PL/SQL

- Using the Data Interface for Persistent LOBs in OCI

- Using the Data Interface for Persistent LOBs in Java

- Using the Data Interface with Remote LOBs

Overview of the Data Interface for Persistent LOBs

The data interface for persistent LOBs includes a set of Java, PL/SQL, and OCI APIs that are extended to work with LOB datatypes. These APIs, originally designed for use with legacy datatypes such as LONG, LONG RAW, and VARCHAR2, can also be used with the corresponding LOB datatypes shown in Table 13-1 and Table 13-2. These tables show the legacy datatypes in the "bind or define type" column and the corresponding supported LOB datatype in the "LOB column type" column. You can use the data interface for LOBs to store and manipulate character data and binary data in a LOB column just as if it were stored in the corresponding legacy datatype.

Note:

The data interface works for LOB columns as well as LOBs which are attributes of objects. In this chapter "LOB columns" means LOB columns and LOB attributes.
You can use array bind and define interfaces to insert and select multiple rows in one round trip.

For simplicity, this chapter focuses on character datatypes; however, the same concepts apply to the full set of character and binary datatypes listed in Table 13-1 and Table 13-2. CLOB also means NCLOB in these tables.

Table 13-1 Corresponding LONG and LOB Datatypes in SQL and PL/SQL

Bind or Define Type

LOB Column Type

Used For Storing

CHAR

CLOB

Character data

LONG

CLOB

Character data

VARCHAR2

CLOB

Character data

LONG RAW

BLOB

Binary data

RAW

BLOB

Binary data

Table 13-2 Corresponding LONG and LOB Datatypes in OCI

Bind or Define Type

LOB Column Type

Used For Storing

SQLT_AFC(n)

CLOB

Character data

SQLT_CHR

CLOB

Character data

SQLT_LNG

CLOB

Character data

SQLT_VCS

CLOB

Character data

SQLT_BIN

BLOB

Binary data

SQLT_LBI

BLOB

Binary data

SQLT_LVB

BLOB

Binary data

Benefits of Using the Data Interface for Persistent LOBs

Using the data interface for persistent LOBs has the following benefits:

- If your application already uses LONG datatypes, then you can use the same application with LOB datatypes with little or no modification of your existing application required. To do so, just convert LONG datatype columns in your tables to LOB datatype columns as discussed in Chapter 11, "Migrating Columns from LONGs to LOBs".

- Performance is better for OCI applications that use sequential access techniques. A piecewise INSERT or fetch using the data interface has comparable performance to using OCI functions like OCILobRead2() and OCILobWrite2(). Because the data interface allows more than 4K bytes of data to be inserted into a LOB in a single OCI call, a round-trip to the server is saved.

- You can read LOB data in one OCIStmtFetch() call, instead of fetching the LOB locator first and then calling OCILobRead2(). This improves performance when you want to read LOB data starting at the beginning.

- You can use array bind and define interfaces to insert and select multiple rows with LOBs in one round trip.

Using the Data Interface for Persistent LOBs in PL/SQL

The data interface enables you to use LONG and LOB datatypes listed in Table 13-1 to perform the following operations in PL/SQL:

- INSERT or UPDATE character data stored in datatypes such as VARCHAR2, CHAR, or LONG into a CLOB column.

- INSERT or UPDATE binary data stored in datatypes such as RAW or LONG RAW into a BLOB column.

- Use the SELECT statement on CLOB columns to select data into a character buffer variable such as CHAR, LONG, or VARCHAR2.

- Use the SELECT statement on BLOB columns to select data into a binary buffer variable such as RAW and LONG RAW.

- Make cross-type assignments (implicit type conversions) between CLOB and VARCHAR2, CHAR, or LONG variables.

- Make cross-type assignments (implicit type conversions) between BLOB and RAW or LONG RAW variables.

- Pass LOB datatypes to functions defined to accept LONG datatypes or pass LONG datatypes to functions defined to accept LOB datatypes. For example, you can pass a CLOB instance to a function defined to accept another character type, such as VARCHAR2, CHAR, or LONG.

- Use CLOBs with other PL/SQL functions and operators that accept VARCHAR2 arguments such as INSTR and SUBSTR. See "Passing CLOBs to SQL and PL/SQL Built-In Functions" for a complete list.

Note:

When using the data interface for LOBs with the SELECT statement in PL/SQL, you cannot specify the amount you want to read. You can only specify the buffer length of your buffer. If your buffer length is smaller than the LOB data length, then the database throws an exception.

See Also:

- Chapter 9, "SQL Semantics and LOBs" for details on LOB support in SQL statements

- "Some Implicit Conversions Are Not Supported for LOB Datatypes"

Guidelines for Accessing LOB Columns Using the Data Interface in SQL and PL/SQL

This section describes techniques you use to access LOB columns or attributes using the data interface for persistent LOBs.

Data from CLOB and BLOB columns or attributes can be referenced by regular SQL statements, such as INSERT, UPDATE, and SELECT.

There is no piecewise INSERT, UPDATE, or fetch routine in PL/SQL. Therefore, the amount of data that can be accessed from a LOB column or attribute is limited by the maximum character buffer size. PL/SQL supports character buffer sizes up to 32KB - 1 (32767 bytes). For this reason, LOB only less than 32K bytes in size can be accessed by PL/SQL applications using the data interface for persistent LOBs.

If you need to access more than 32KB -1 using the data interface, then you must make OCI calls from the PL/SQL code to use the APIs for piecewise insert and fetch.

Use he following are guidelines for using the data interface to access LOB columns or attributes:

- INSERT operations

You can INSERT into tables containing LOB columns or attributes using regular INSERT statements in the VALUES clause. The field of the LOB column can be a literal, a character datatype, a binary datatype, or a LOB locator.

- UPDATE operations

LOB columns or attributes can be updated as a whole by UPDATE... SET statements. In the SET clause, the new value can be a literal, a character datatype, a binary datatype, or a LOB locator.

- 4000 byte limit on hexadecimal to raw and raw to hexadecimal conversions

The database does not do implicit hexadecimal to RAW or RAW to hexadecimal conversions on data that is more than 4000 bytes in size. You cannot bind a buffer of character data to a binary datatype column, and you cannot bind a buffer of binary data to a character datatype column if the buffer is over 4000 bytes in size. Attempting to do so will result in your column data being truncated at 4000 bytes.

For example, you cannot bind a VARCHAR2 buffer to a LONG RAW or a BLOB column if the buffer is more than 4000 bytes in size. Similarly, you cannot bind a RAW buffer to a LONG or a CLOB column if the buffer is more than 4000 bytes in size.

- SELECT operations

LOB columns or attributes can be selected into character or binary buffers in PL/SQL. If the LOB column or attribute is longer than the buffer size, then an exception is raised without filling the buffer with any data. LOB columns or attributes can also be selected into LOB locators.

Implicit Assignment and Parameter Passing

Implicit assignment and parameter passing are supported for LOB columns. For the datatypes listed in Table 13-1 and Table 13-2, you can pass or assign: any character type to any other character type, or any binary type to any other binary type using the data interface for persistent LOBs.

Implicit assignment works for variables declared explicitly and for variables declared by referencing an existing column type using the %TYPE attribute as show in the following example. This example assumes that column long_col in table t has been migrated from a LONG to a CLOB column.

CREATE TABLE t (long_col LONG); -- Alter this table to change LONG column to LOB
DECLARE
a VARCHAR2(100);
b t.long_col%type; -- This variable changes from LONG to CLOB
BEGIN
SELECT * INTO b FROM t;
a := b;  -- This changes from "VARCHAR2 := LONG to VARCHAR2 := CLOB
b := a;  -- This changes from "LONG := VARCHAR2 to CLOB := VARCHAR2
END;

Implicit parameter passing is allowed between functions and procedures. For example, you can pass a CLOB to a function or procedure where the formal parameter is defined as a VARCHAR2.

Note:

The assigning a VARCHAR2 buffer to a LOB variable is somewhat less efficient than assigning a VARCHAR2 to a LONG variable because the former involves creating a temporary LOB. Therefore, PL/SQL users will see a slight deterioration in the performance of their applications.

Passing CLOBs to SQL and PL/SQL Built-In Functions

Implicit parameter passing is also supported for built-in PL/SQL functions that accept character data. For example, INSTR can accept a CLOB as well as other character data.

Any SQL or PL/SQL built-in function that accepts a VARCHAR2 can accept a CLOB as an argument. Similarly, a VARCHAR2 variable can be passed to any DBMS_LOB API for any parameter that takes a LOB locator.

See Also:

Chapter 9, "SQL Semantics and LOBs"

Explicit Conversion Functions

In PL/SQL, the following explicit conversion functions convert other data types to CLOB and BLOB datatypes as follows:

- TO_CLOB() converts LONG, VARCHAR2, and CHAR to CLOB

- TO_BLOB() converts LONG RAW and RAW to BLOB

Also note that the conversion function TO_CHAR() can convert a CLOB to a CHAR type.

Calling PL/SQL and C Procedures from SQL

When a PL/SQL or C procedure is called from SQL, buffers with more than 4000 bytes of data are not allowed.

Calling PL/SQL and C Procedures from PL/SQL

You can call a PL/SQL or C procedure from PL/SQL. You can pass a CLOB as an actual parameter where CHR is the formal parameter, or vice versa. The same holds for BLOBs and RAWs.

One example of when these cases can arise is when either the formal or the actual parameter is an anchored type, that is, the variable is declared using the table_name.column_name%type syntax.

PL/SQL procedures or functions can accept a CLOB or a VARCHAR2 as a formal parameter. For example the PL/SQL procedure could be one of the following:

- When the formal parameter is a CLOB:

CREATE OR REPLACE PROCEDURE get_lob(table_name IN VARCHAR2, lob INOUT
CLOB) AS
...
BEGIN
...
END;
/

- When the formal parameter is a VARCHAR2:

CREATE OR REPLACE PROCEDURE get_lob(table_name IN VARCHAR2, lob INOUT
VARCHAR2) AS
...
BEGIN
...
END;
/

The calling function could be of any of the following types:

- When the actual parameter is a CHR:

create procedure ...
declare
c VARCHAR2[200];
BEGIN
get_lob('table_name', c);
END;

- When the actual parameter is a CLOB:

create procedure ...
declare
c CLOB;
BEGIN
get_lob('table_name', c);
END;

Binds of All Sizes in INSERT and UPDATE Operations

Binds of all sizes are supported for INSERT and UPDATE operations on LOB columns. Multiple binds of any size are allowed in a single INSERT or UPDATE statement.

Note:

When you create a table, the length of the default value you specify for any LOB column is restricted to 4000 bytes.

4000 Byte Limit on Results of a SQL Operator

If you bind more than 4000 bytes of data to a BLOB or a CLOB, and the data consists of a SQL operator, then Oracle Database limits the size of the result to at most 4000 bytes.

The following statement inserts only 4000 bytes because the result of LPAD is limited to 4000 bytes:

INSERT INTO print_media (ad_sourcetext) VALUES (lpad('a', 5000, 'a'));

The following statement inserts only 2000 bytes because the result of LPAD is limited to 4000 bytes, and the implicit hexadecimal to raw conversion converts it to 2000 bytes of RAW data:

INSERT INTO print_media (ad_photo) VALUES (lpad('a', 5000, 'a'));

Example of 4000 Byte Result Limit of a SQL Operator

The following example illustrates how the result for SQL operators is limited to 4000 bytes.

/* The following command inserts only 4000 bytes because the result of
* LPAD is limited to 4000 bytes */
INSERT INTO print_media(product_id, ad_id, ad_sourcetext)
VALUES (2004, 5, lpad('a', 5000, 'a'));
SELECT LENGTH(ad_sourcetext) FROM print_media
WHERE product_id=2004 AND ad_id=5;
ROLLBACK;

/* The following command inserts only 2000 bytes because the result of
* LPAD is limited to 4000 bytes, and the implicit hex to raw conversion
* converts it to 2000 bytes of RAW data. */
INSERT INTO print_media(product_id, ad_id, ad_composite)
VALUES (2004, 5, lpad('a', 5000, 'a'));
SELECT LENGTH(ad_composite) from print_media
WHERE product_id=2004 AND ad_id=5;
ROLLBAACK;

Restrictions on Binds of More Than 4000 Bytes

The following lists the restrictions for binds of more than 4000 bytes:

- If a table has both LONG and LOB columns, then you can bind more than 4000 bytes of data to either the LONG or LOB columns, but not both in the same statement.

- In an INSERT AS SELECT operation, binding of any length data to LOB columns is not allowed.

Parallel DML Support for LOBs

Parallel execution of the following DML operations on tables with LOB columns is supported. These operations run in parallel execution mode only when performed on a partitioned table. DML statements on non-partitioned tables with LOB columns continue to execute in serial execution mode.

- INSERT AS SELECT

- CREATE TABLE AS SELECT

- DELETE

- UPDATE

- MERGE (conditional UPDATE and INSERT)

- Multitable INSERT

See Also:

Oracle Database Administrator's Guide section "Managing Processes for Parallel SQL Execution"

Example: PL/SQL - Using Binds of More Than 4000 Bytes in INSERT and UPDATE

DECLARE
bigtext VARCHAR2(32767);
smalltext VARCHAR2(2000);
bigraw RAW (32767);
BEGIN
bigtext := LPAD('a', 32767, 'a');
smalltext := LPAD('a', 2000, 'a');
bigraw := utl_raw.cast_to_raw (bigtext);

/* Multiple long binds for LOB columns are allowed for INSERT: */
INSERT INTO print_media(product_id, ad_id, ad_sourcetext, ad_composite)
VALUES (2004, 1, bigtext, bigraw);

/* Single long bind for LOB columns is allowed for INSERT: */
INSERT INTO print_media (product_id, ad_id, ad_sourcetext)
VALUES (2005, 2, smalltext);

bigtext := LPAD('b', 32767, 'b');
smalltext := LPAD('b', 20, 'a');
bigraw := utl_raw.cast_to_raw (bigtext);

/* Multiple long binds for LOB columns are allowed for UPDATE: */
UPDATE print_media SET ad_sourcetext = bigtext, ad_composite = bigraw,
ad_finaltext = smalltext;

/* Single long bind for LOB columns is allowed for UPDATE: */
UPDATE print_media SET ad_sourcetext = smalltext, ad_finaltext = bigtext;

/* The following is NOT allowed because we are trying to insert more than
4000 bytes of data in a LONG and a LOB column: */
INSERT INTO print_media(product_id, ad_id, ad_sourcetext, press_release)
VALUES (2030, 3, bigtext, bigtext);

/* Insert of data into LOB attribute is allowed */
INSERT INTO print_media(product_id, ad_id, ad_header)
VALUES (2049, 4, adheader_typ(null, null, null, bigraw));

/* The following is not allowed because we try to perform INSERT AS
SELECT data INTO LOB */
INSERT INTO print_media(product_id, ad_id, ad_sourcetext)
SELECT 2056, 5, bigtext FROM dual;

END;
/

Using the Data Interface for LOBs with INSERT, UPDATE, and SELECT Operations

INSERT and UPDATE statements on LOBs are used in the same way as on LONGs. For example:

DECLARE
ad_buffer VARCHAR2(100);
BEGIN
INSERT INTO print_media(product_id, ad_id, ad_sourcetext)
VALUES(2004, 5, 'Source for advertisement 1');
UPDATE print_media SET ad_sourcetext= 'Source for advertisement 2'
WHERE product_id=2004 AND ad_id=5;
/* This will get the LOB column if it is up to 100 bytes, otherwise it will
* raise an exception */
SELECT ad_sourcetext INTO ad_buffer FROM print_media
WHERE product_id=2004 AND ad_id=5;
END;
/

Using the Data Interface for LOBs in Assignments and Parameter Passing

The data interface for LOBs enables implicit assignment and parameter passing as shown in the following example:

CREATE TABLE t (clob_col CLOB, blob_col BLOB);
INSERT INTO t VALUES('abcdefg', 'aaaaaa');

DECLARE
var_buf VARCHAR2(100);
clob_buf CLOB;
raw_buf RAW(100);
blob_buf BLOB;
BEGIN
SELECT * INTO clob_buf, blob_buf FROM t;
var_buf := clob_buf;
clob_buf:= var_buf;
raw_buf := blob_buf;
blob_buf := raw_buf;
END;
/

CREATE OR REPLACE PROCEDURE FOO ( a IN OUT CLOB) IS
BEGIN
-- Any procedure body
a := 'abc';
END;
/

CREATE OR REPLACE PROCEDURE BAR (b IN OUT VARCHAR2) IS
BEGIN
-- Any procedure body
b := 'xyz';
END;
/

DECLARE
a VARCHAR2(100) := '1234567';
b CLOB;
BEGIN
FOO(a);
SELECT clob_col INTO b FROM t;
BAR(b);
END;
/

Using the Data Interface for LOBs with PL/SQL Built-In Functions

This example illustrates the use of CLOBs in PL/SQL built-in functions, using the data interface for LOBs:

DECLARE
my_ad CLOB;
revised_ad CLOB;
myGist VARCHAR2(100):= 'This is my gist.';
revisedGist VARCHAR2(100);
BEGIN
INSERT INTO print_media (product_id, ad_id, ad_sourcetext)
VALUES (2004, 5, 'Source for advertisement 1');

-- select a CLOB column into a CLOB variable
SELECT ad_sourcetext INTO my_ad FROM print_media
WHERE product_id=2004 AND ad_id=5;

-- perform VARCHAR2 operations on a CLOB variable
revised_ad := UPPER(SUBSTR(my_ad, 1, 20));

-- revised_ad is a temporary LOB
-- Concat a VARCHAR2 at the end of a CLOB
revised_ad := revised_ad || myGist;

-- The following statement will raise an error if my_ad is
-- longer than 100 bytes
myGist := my_ad;
END;
/

Using the Data Interface for Persistent LOBs in OCI

This section discusses OCI functions included in the data interface for persistent LOBs. These OCI functions work for LOB datatypes exactly the same way as they do for LONG datatypes. Using these functions, you can perform INSERT, UPDATE, fetch, bind, and define operations in OCI on LOBs using the same techniques you would use on other datatypes that store character or binary data.

Note:

You can use array bind and define interfaces to insert and select multiple rows with LOBs in one round trip.

See Also:

Oracle Call Interface Programmer's Guide, chapter 5, section "Runtime Data Allocation and Piecewise Operations in OCI"

Binding LOB Datatypes in OCI

You can bind LOB datatypes in the following operations:

- Regular, piecewise, and callback binds for INSERT and UPDATE operations

- Array binds for INSERT and UPDATE operations

- Parameter passing across PL/SQL and OCI boundaries

Piecewise operations can be performed by polling or by providing a callback. To support these operations, the following OCI functions accept the LONG and LOB datatypes listed in Table 13-2.

- OCIBindByName() and OCIBindByPos()

These functions create an association between a program variable and a placeholder in the SQL statement or a PL/SQL block for INSERT and UPDATE operations.

- OCIBindDynamic()

You use this call to register callbacks for dynamic data allocation for INSERT and UPDATE operations

- OCIStmtGetPieceInfo() and OCIStmtSetPieceInfo()

These calls are used to get or set piece information for piecewise operations.

Defining LOB Datatypes in OCI

The data interface for persistent LOBs allows the following OCI functions to accept the LONG and LOB datatypes listed in Table 13-2.

- OCIDefineByPos()

This call associates an item in a SELECT list with the type and output data buffer.

- OCIDefineDynamic()

This call registers user callbacks for SELECT operations if the OCI_DYNAMIC_FETCH mode was selected in OCIDefineByPos() function call.

When you use these functions with LOB types, the LOB data, and not the locator, is selected into your buffer. Note that in OCI, you cannot specify the amount you want to read using the data interface for LOBs. You can only specify the buffer length of your buffer. The database only reads whatever amount fits into your buffer and the data is truncated.

Using Multibyte Character Sets in OCI with the Data Interface for LOBs

When the client character set is in a multibyte format, functions included in the data interface operate the same way with LOB datatypes as they do for LONG datatypes as follows:

- For a piecewise fetch in a multibyte character set, a multibyte character could be cut in the middle, with some bytes at the end of one buffer and remaining bytes in the next buffer.

- For a regular fetch, if the buffer cannot hold all bytes of the last character, then Oracle returns as many bytes as fit into the buffer, hence returning partial characters.

Using OCI Functions to Perform INSERT or UPDATE on LOB Columns

This section discusses the various techniques you can use to perform INSERT or UPDATE operations on LOB columns or attributes using the data interface. The operations described in this section assume that you have initialized the OCI environment and allocated all necessary handles.

Simple INSERTs or UPDATEs in One Piece

To perform simple INSERT or UPDATE operations in one piece using the data interface for persistent LOBs, perform the following steps:

1. Call OCIStmtPrepare() to prepare the statement in OCI_DEFAULT mode.

2. Call OCIBindByName() or OCIBindbyPos() in OCI_DEFAULT mode to bind a placeholder for LOB as character data or binary data.

3. Call OCIStmtExecute() to do the actual INSERT or UPDATE operation.

Using Piecewise INSERTs and UPDATEs with Polling

To perform piecewise INSERT or UPDATE operations with polling using the data interface for persistent LOBs, do the following steps:

1. Call OCIStmtPrepare() to prepare the statement in OCI_DEFAULT mode.

2. Call OCIBindByName() or OCIBindbyPos() in OCI_DATA_AT_EXEC mode to bind a LOB as character data or binary data.

3. Call OCIStmtExecute() in default mode. Do each of the following in a loop while the value returned from OCIStmtExecute() is OCI_NEED_DATA. Terminate your loop when the value returned from OCIStmtExecute() is OCI_SUCCESS.

- Call OCIStmtGetPieceInfo() to retrieve information about the piece to be inserted.

- Call OCIStmtSetPieceInfo() to set information about piece to be inserted.

Piecewise INSERTs and UPDATEs with Callback

To perform piecewise INSERT or UPDATE operations with callback using the data interface for persistent LOBs, do the following steps:

1. Call OCIStmtPrepare() to prepare the statement in OCI_DEFAULT mode.

2. Call OCIBindByName() or OCIBindbyPos() in OCI_DATA_AT_EXEC mode to bind a placeholder for the LOB column as character data or binary data.

3. Call OCIBindDynamic() to specify the callback.

4. Call OCIStmtExecute() in default mode.

Array INSERT and UPDATE Operations

To perform array INSERT or UPDATE operations using the data interface for persistent LOBs, use any of the techniques discussed in this section in conjunction with OCIBindArrayOfStruct(), or by specifying the number of iterations (iter), with iter value greater than 1, in the OCIStmtExecute() call.

Using the Data Interface to Fetch LOB Data in OCI

This section discusses techniques you can use to fetch data from LOB columns or attributes in OCI using the data interface for persistent LOBs.

Simple Fetch in One Piece

To perform a simple fetch operation on LOBs in one piece using the data interface for persistent LOBs, do the following:

1. Call OCIStmtPrepare() to prepare the SELECT statement in OCI_DEFAULT mode.

2. Call OCIDefineByPos() to define a select list position in OCI_DEFAULT mode to define a LOB as character data or binary data.

3. Call OCIStmtExecute() to run the SELECT statement.

4. Call OCIStmtFetch() to do the actual fetch.

Piecewise Fetch with Polling

To perform a piecewise fetch operation on a LOB column with polling using the data interface for LOBs, do the following steps:

1. Call OCIStmtPrepare() to prepare the SELECT statement in OCI_DEFAULT mode.

2. Call OCIDefinebyPos() to define a select list position in OCI_DYNAMIC_FETCH mode to define the LOB column as character data or binary data.

3. Call OCIStmtExecute() to run the SELECT statement.

4. Call OCIStmtFetch() in default mode. Do each of the following in a loop while the value returned from OCIStmtFetch() is OCI_NEED_DATA. Terminate your loop when the value returned from OCIStmtFetch() is OCI_SUCCESS.

- Call OCIStmtGetPieceInfo() to retrieve information about the piece to be fetched.

- Call OCIStmtSetPieceInfo() to set information about piece to be fetched.

Piecewise with Callback

To perform a piecewise fetch operation on a LOB column with callback using the data interface for persistent LOBs, do the following:

1. Call OCIStmtPrepare() to prepare the statement in OCI_DEFAULT mode.

2. Call OCIDefinebyPos() to define a select list position in OCI_DYNAMIC_FETCH mode to define the LOB column as character data or binary data.

3. Call OCIStmtExecute() to run the SELECT statement.

4. Call OCIDefineDynamic() to specify the callback.

5. Call OCIStmtFetch() in default mode.

Array Fetch

To perform an array fetch in OCI using the data interface for persistent LOBs, use any of the techniques discussed in this section in conjunction with OCIDefineArrayOfStruct(), or by specifying the number of iterations (iter), with the value of iter greater than 1, in the OCIStmtExecute() call.

PL/SQL and C Binds from OCI

When you call a PL/SQL procedure from OCI, and have an in or out or in/out bind, you should be able to:

- Bind a variable as SQLT_CHR or SQLT_LNG where the formal parameter of the PL/SQL procedure is SQLT_CLOB, or

- Bind a variable as SQLT_BIN or SQLT_LBI where the formal parameter is SQLT_BLOB

The following two cases work:

Calling PL/SQL Out-binds in the "begin foo(:1); end;" Manner

Here is an example of calling PL/SQL out-binds in the "begin foo(:1); end;" Manner:

text *sqlstmt = (text *)"BEGIN get_lob(:c); END; " ;

Calling PL/SQL Out-binds in the "call foo(:1);" Manner

Here is an example of calling PL/SQL out-binds in the "call foo(:1);" manner:

text *sqlstmt = (text *)"CALL get_lob( :c );" ;

In both these cases, the rest of the program has these statements:

OCIStmtPrepare(stmthp, errhp, sqlstmt, (ub4)strlen((char *)sqlstmt),
(ub4) OCI_NTV_SYNTAX, (ub4) OCI_DEFAULT);
curlen = 0;
OCIBindByName(stmthp, &bndhp[3], errhp,
(text *) ":c", (sb4) strlen((char *) ":c"),
(dvoid *) buf5, (sb4) LONGLEN, SQLT_CHR,
(dvoid *) 0, (ub2 *) 0, (ub2 *) 0,
(ub4) 1, (ub4 *) &curlen, (ub4) OCI_DATA_AT_EXEC);

The PL/SQL procedure, get_lob(), is as follows:

procedure get_lob(c INOUT CLOB) is  -- This might have been column%type
BEGIN
... /* The procedure body could be in PL/SQL or C*/
END;

Example: C (OCI) - Binds of More than 4000 Bytes for INSERT and UPDATE

void insert3()
{
/* Insert of data into LOB attributes is allowed. */
ub1 buffer[8000];
text *insert_sql = (text *)"INSERT INTO Print_media (ad_header) \
VALUES (adheader_typ(NULL, NULL, NULL,:1))";
OCIStmtPrepare(stmthp, errhp, insert_sql, strlen((char*)insert_sql),
(ub4) OCI_NTV_SYNTAX, (ub4) OCI_DEFAULT);
OCIBindByPos(stmthp, &bindhp[0], errhp, 1, (dvoid *)buffer, 2000,
SQLT_LNG, 0, 0, 0, 0, 0, (ub4) OCI_DEFAULT);
OCIStmtExecute(svchp, stmthp, errhp, 1, 0, (const OCISnapshot*) 0,
(OCISnapshot*)0, OCI_DEFAULT);
}

Using the Data Interface for LOBs in PL/SQL Binds from OCI on LOBs

The data interface for LOBs allows LOB PL/SQL binds from OCI to work as follows. When you call a PL/SQL procedure from OCI, and have an IN or OUT or IN OUT bind, you should be able to bind a variable as SQLT_CHR, where the formal parameter of the PL/SQL procedure is SQLT_CLOB.

Note:

C procedures are wrapped inside a PL/SQL stub, so the OCI application always calls the PL/SQL stub.

For the OCI calling program, the following are likely cases:

Calling PL/SQL Out-binds in the "begin foo(:1); end;" Manner

For example:

text *sqlstmt = (text *)"BEGIN PKG1.P5 (:c); END; " ;

Calling PL/SQL Out-binds in the "call foo(:1);" Manner

For example:

text *sqlstmt = (text *)"CALL PKG1.P5( :c );" ;

In both these cases, the rest of the program is as follows:

OCIStmtPrepare(stmthp, errhp, sqlstmt, (ub4)strlen((char *)sqlstmt),
(ub4) OCI_NTV_SYNTAX, (ub4) OCI_DEFAULT);
curlen = 0;

OCIBindByName(stmthp, &bndhp[3], errhp,
(text *) ":c4", (sb4) strlen((char *) ":c"),
(dvoid *) buf5, (sb4) LONGLEN, SQLT_CHR,
(dvoid *) 0, (ub2 *) 0, (ub2 *) 0,
(ub4) 1, (ub4 *) &curlen, (ub4) OCI_DATA_AT_EXEC);

OCIStmtExecute(svchp, stmthp, errhp,(ub4) 0,(ub4) 0, (const OCISnapshot*) 0,
(OCISnapshot*) 0,(ub4) OCI_DEFAULT);

The PL/SQL procedure PKG1.P5 is as follows:

CREATE OR REPLACE PACKAGE BODY pkg1 AS
...
procedure p5 (c OUT CLOB) is
-- This might have been table%rowtype (so it   is CLOB now)
BEGIN
...
END p5;

END pkg1;

Binding LONG Data for LOB Columns in Binds Greater Than 4000 Bytes

The following example illustrates binding character data for a LOB column:

void simple_insert()
{
word buflen;
text buf[5000];
text *insstmt = (text *) "INSERT INTO Print_media(Product_id, Ad_id,\
Ad_sourcetext) VALUES (2004, 1, :SRCTXT)";

OCIStmtPrepare(stmthp, errhp, insstmt, (ub4)strlen((char *)insstmt),
(ub4) OCI_NTV_SYNTAX, (ub4) OCI_DEFAULT);

OCIBindByName(stmthp, &bndhp[0], errhp,
(text *) ":SRCTXT", (sb4) strlen((char *) ":SRCTXT"),
(dvoid *) buf, (sb4) sizeof(buf), SQLT_CHR,
(dvoid *) 0, (ub2 *) 0, (ub2 *) 0,
(ub4) 0, (ub4 *) 0, (ub4) OCI_DEFAULT);

memset((void *)buf, (int)'A', (size_t)5000);
OCIStmtExecute(svchp, stmthp, errhp, (ub4) 1, (ub4) 0,
(const OCISnapshot*) 0, (OCISnapshot*) 0, (ub4) OCI_DEFAULT);
}

Binding LONG Data to LOB Columns Using Piecewise INSERT with Polling

The following example illustrates using piecewise INSERT with polling using the data interface for LOBs.

void piecewise_insert()
{
text *sqlstmt = (text *)"INSERT INTO Print_media(Product_id, Ad_id,\
Ad_sourcetext) VALUES (:1, :2, :3)";
ub2 rcode;
ub1 piece, i;
word product_id = 2004;
word ad_id = 2;
ub4 buflen;
char buf[5000];

OCIStmtPrepare(stmthp, errhp, sqlstmt, (ub4)strlen((char *)sqlstmt),
(ub4) OCI_NTV_SYNTAX, (ub4) OCI_DEFAULT);
OCIBindByPos(stmthp, &bndhp[0], errhp, (ub4) 1,
(dvoid *) &product_id, (sb4) sizeof(product_id), SQLT_INT,
(dvoid *) 0, (ub2 *)0, (ub2 *)0,
(ub4) 0, (ub4 *) 0, (ub4) OCI_DEFAULT);
OCIBindByPos(stmthp, &bndhp[1], errhp, (ub4) 2,
(dvoid *) &ad_id, (sb4) sizeof(ad_id), SQLT_INT,
(dvoid *) 0, (ub2 *)0, (ub2 *)0,
(ub4) 0, (ub4 *) 0, (ub4) OCI_DEFAULT);
OCIBindByPos(stmthp, &bndhp[2], errhp, (ub4) 3,
(dvoid *) 0, (sb4) 15000, SQLT_LNG,
(dvoid *) 0, (ub2 *)0, (ub2 *)0,
(ub4) 0, (ub4 *) 0, (ub4) OCI_DATA_AT_EXEC);

i = 0;
while (1)
{
i++;
retval = OCIStmtExecute(svchp, stmthp, errhp, (ub4) 1, (ub4) 0,
(CONST OCISnapshot*) 0, (OCISnapshot*) 0,
(ub4) OCI_DEFAULT);
switch(retval)
{
case OCI_NEED_DATA:
memset((void *)buf, (int)'A'+i, (size_t)5000);
buflen = 5000;
if (i == 1) piece = OCI_FIRST_PIECE;
else if (i == 3) piece = OCI_LAST_PIECE;
else piece = OCI_NEXT_PIECE;

if (OCIStmtSetPieceInfo((dvoid *)bndhp[2],
(ub4)OCI_HTYPE_BIND, errhp, (dvoid *)buf,
&buflen, piece, (dvoid *) 0, &rcode))
{
DISCARD printf("ERROR: OCIStmtSetPieceInfo: %d \n", retval);
break;
}

break;
case OCI_SUCCESS:
break;
default:
printf( "oci exec returned %d \n", retval);
report_error(errhp);
retval = OCI_SUCCESS;
} /* end switch */
if (retval == OCI_SUCCESS)
break;
} /* end while(1) */
}

Binding LONG Data to LOB Columns Using Piecewise INSERT with Callback

The following example illustrates binding LONG data to LOB columns using a piecewise INSERT with callback:

void callback_insert()
{
word buflen = 15000;
word product_id = 2004;
word ad_id = 3;
text *sqlstmt = (text *) "INSERT INTO Print_media(Product_id, Ad_id,\
Ad_sourcetext) VALUES (:1, :2, :3)";
word pos = 3;

OCIStmtPrepare(stmthp, errhp, sqlstmt, (ub4)strlen((char *)sqlstmt),
(ub4) OCI_NTV_SYNTAX, (ub4) OCI_DEFAULT)

OCIBindByPos(stmthp, &bndhp[0], errhp, (ub4) 1,
(dvoid *) &product_id, (sb4) sizeof(product_id), SQLT_INT,
(dvoid *) 0, (ub2 *)0, (ub2 *)0,
(ub4) 0, (ub4 *) 0, (ub4) OCI_DEFAULT);
OCIBindByPos(stmthp, &bndhp[1], errhp, (ub4) 2,
(dvoid *) &ad_id, (sb4) sizeof(ad_id), SQLT_INT,
(dvoid *) 0, (ub2 *)0, (ub2 *)0,
(ub4) 0, (ub4 *) 0, (ub4) OCI_DEFAULT);
OCIBindByPos(stmthp, &bndhp[2], errhp, (ub4) 3,
(dvoid *) 0, (sb4) buflen, SQLT_CHR,
(dvoid *) 0, (ub2 *)0, (ub2 *)0,
(ub4) 0, (ub4 *) 0, (ub4) OCI_DATA_AT_EXEC);

OCIBindDynamic(bndhp[2], errhp, (dvoid *) (dvoid *) &pos,
insert_cbk, (dvoid *) 0, (OCICallbackOutBind) 0);

OCIStmtExecute(svchp, stmthp, errhp, (ub4) 1, (ub4) 0,
(const OCISnapshot*) 0, (OCISnapshot*) 0,
(ub4) OCI_DEFAULT);
} /* end insert_data() */

/* Inbind callback to specify input data. */
static sb4 insert_cbk(dvoid *ctxp, OCIBind *bindp, ub4 iter, ub4 index,
dvoid **bufpp, ub4 *alenpp, ub1 *piecep, dvoid **indpp)
{
static int a = 0;
word   j;
ub4    inpos = *((ub4 *)ctxp);
char   buf[5000];

switch(inpos)
{
case 3:
memset((void *)buf, (int) 'A'+a, (size_t) 5000);
*bufpp = (dvoid *) buf;
*alenpp = 5000 ;
a++;
break;
default: printf("ERROR: invalid position number: %d\n", inpos);
}

*indpp = (dvoid *) 0;
*piecep = OCI_ONE_PIECE;
if (inpos == 3)
{
if (a<=1)
{
*piecep = OCI_FIRST_PIECE;
printf("Insert callback: 1st piece\n");
}
else if (a<3)
{
*piecep = OCI_NEXT_PIECE;
printf("Insert callback: %d'th piece\n", a);
}
else {
*piecep = OCI_LAST_PIECE;
printf("Insert callback: %d'th piece\n", a);
a = 0;
}
}
return OCI_CONTINUE;
}

Binding LONG Data to LOB Columns Using an Array INSERT

The following example illustrates binding character data for LOB columns using an array INSERT operation:

void array_insert()
{
ub4 i;
word buflen;
word arrbuf1[5];
word arrbuf2[5];
text arrbuf3[5][5000];
text *insstmt = (text *)"INSERT INTO Print_media(Product_id, Ad_id,\
Ad_sourcetext) VALUES (:PID, :AID, :SRCTXT)";

OCIStmtPrepare(stmthp, errhp, insstmt,
(ub4)strlen((char *)insstmt), (ub4) OCI_NTV_SYNTAX,
(ub4) OCI_DEFAULT);

OCIBindByName(stmthp, &bndhp[0], errhp,
(text *) ":PID", (sb4) strlen((char *) ":PID"),
(dvoid *) &arrbuf1[0], (sb4) sizeof(arrbuf1[0]), SQLT_INT,
(dvoid *) 0, (ub2 *)0, (ub2 *) 0,
(ub4) 0, (ub4 *) 0, (ub4) OCI_DEFAULT);

OCIBindByName(stmthp, &bndhp[1], errhp,
(text *) ":AID", (sb4) strlen((char *) ":AID"),
(dvoid *) &arrbuf2[0], (sb4) sizeof(arrbuf2[0]), SQLT_INT,
(dvoid *) 0, (ub2 *)0, (ub2 *) 0,
(ub4) 0, (ub4 *) 0, (ub4) OCI_DEFAULT);

OCIBindByName(stmthp, &bndhp[2], errhp,
(text *) ":SRCTXT", (sb4) strlen((char *) ":SRCTXT"),
(dvoid *) arrbuf3[0], (sb4) sizeof(arrbuf3[0]), SQLT_CHR,
(dvoid *) 0, (ub2 *) 0, (ub2 *) 0,
(ub4) 0, (ub4 *) 0, (ub4) OCI_DEFAULT);

OCIBindArrayOfStruct(bndhp[0], errhp sizeof(arrbuf1[0]),
indsk, rlsk, rcsk);
OCIBindArrayOfStruct(bndhp[1], errhp, sizeof(arrbuf2[0]),
indsk, rlsk, rcsk);
OCIBindArrayOfStruct(bndhp[2], errhp, sizeof(arrbuf3[0]),
indsk, rlsk, rcsk);

for (i=0; i<5; i++)
{
arrbuf1[i] = 2004;
arrbuf2[i] = i+4;
memset((void *)arrbuf3[i], (int)'A'+i, (size_t)5000);
}
OCIStmtExecute(svchp, stmthp, errhp, (ub4) 5, (ub4) 0,
(const OCISnapshot*) 0, (OCISnapshot*) 0,
(ub4) OCI_DEFAULT);

}

Selecting a LOB Column into a LONG Buffer Using a Simple Fetch

The following example illustrates selecting a LOB column using a simple fetch:

void simple_fetch()
{
word retval;
text buf[15000];
text *selstmt = (text *) "SELECT Ad_sourcetext FROM Print_media WHERE\
Product_id = 2004";

OCIStmtPrepare(stmthp, errhp, selstmt, (ub4)strlen((char *)selstmt),
(ub4) OCI_NTV_SYNTAX, (ub4) OCI_DEFAULT);

retval = OCIStmtExecute(svchp, stmthp, errhp, (ub4) 0, (ub4) 0,
(const OCISnapshot*) 0, (OCISnapshot*) 0,
(ub4) OCI_DEFAULT);
while (retval == OCI_SUCCESS || retval == OCI_SUCCESS_WITH_INFO)
{
OCIDefineByPos(stmthp, &defhp, errhp, (ub4) 1, (dvoid *) buf,
(sb4) sizeof(buf), (ub2) SQLT_CHR, (dvoid *) 0,
(ub2 *) 0, (ub2 *) 0, (ub4) OCI_DEFAULT);
retval = OCIStmtFetch(stmthp, errhp, (ub4) 1,
(ub4) OCI_FETCH_NEXT, (ub4) OCI_DEFAULT);
if (retval == OCI_SUCCESS || retval == OCI_SUCCESS_WITH_INFO)
DISCARD printf("buf = %.*s\n", 15000, buf);
}
}

Selecting a LOB Column into a LONG Buffer Using Piecewise Fetch with Polling

The following example illustrates selecting a LOB column into a LONG buffer using a piecewise fetch with polling:

void piecewise_fetch()
{
text buf[15000];
ub4 buflen=5000;
word retval;
text *selstmt = (text *) "SELECT Ad_sourcetext FROM Print_media\
WHERE Product_id = 2004 AND Ad_id = 2";

OCIStmtPrepare(stmthp, errhp, selstmt,
(ub4) strlen((char *)selstmt),
(ub4) OCI_NTV_SYNTAX, (ub4) OCI_DEFAULT);

OCIDefineByPos(stmthp, &dfnhp, errhp, (ub4) 1,
(dvoid *) NULL, (sb4) 100000, SQLT_LNG,
(dvoid *) 0, (ub2 *) 0,
(ub2 *) 0, (ub4) OCI_DYNAMIC_FETCH);

retval = OCIStmtExecute(svchp, stmthp, errhp, (ub4) 0, (ub4) 0,
(CONST OCISnapshot*) 0, (OCISnapshot*) 0,
(ub4) OCI_DEFAULT);

retval = OCIStmtFetch(stmthp, errhp, (ub4) 1 ,
(ub2) OCI_FETCH_NEXT, (ub4) OCI_DEFAULT);

while (retval != OCI_NO_DATA && retval != OCI_SUCCESS)
{
ub1 piece;
ub4 iter;
ub4 idx;

genclr((void *)buf, 5000);
switch(retval)
{
case OCI_NEED_DATA:
OCIStmtGetPieceInfo(stmthp, errhp, &hdlptr, &hdltype,
&in_out, &iter, &idx, &piece);
buflen = 5000;
OCIStmtSetPieceInfo(hdlptr, hdltype, errhp,
(dvoid *) buf, &buflen, piece,
(CONST dvoid *) &indp1, (ub2 *) 0);
retval = OCI_NEED_DATA;
break;
default:
printf("ERROR: piece-wise fetching, %d\n", retval);
return;
} /* end switch */
retval = OCIStmtFetch(stmthp, errhp, (ub4) 1 ,
(ub2) OCI_FETCH_NEXT, (ub4) OCI_DEFAULT);
printf("Data : %.5000s\n", buf);
} /* end while */
}

Selecting a LOB Column into a LONG Buffer Using Piecewise Fetch with Callback

The following example illustrates selecting a LONG column into a LOB buffer when using a piecewise fetch with callback:

char buf[5000];
void callback_fetch()
{
word outpos = 1;
text *sqlstmt = (text *) "SELECT Ad_sourcetext FROM Print_media WHERE\
Product_id = 2004 AND Ad_id = 3";

OCIStmtPrepare(stmthp, errhp, sqlstmt, (ub4)strlen((char *)sqlstmt),
(ub4) OCI_NTV_SYNTAX, (ub4) OCI_DEFAULT);
OCIDefineByPos(stmthp, &dfnhp[0], errhp, (ub4) 1,
(dvoid *) 0, (sb4)3 * sizeof(buf), SQLT_CHR,
(dvoid *) 0, (ub2 *)0, (ub2 *)0,
(ub4) OCI_DYNAMIC_FETCH);

OCIDefineDynamic(dfnhp[0], errhp, (dvoid *) &outpos,
(OCICallbackDefine) fetch_cbk);

OCIStmtExecute(svchp, stmthp, errhp, (ub4) 1, (ub4) 0,
(const OCISnapshot*) 0, (OCISnapshot*) 0,
(ub4) OCI_DEFAULT);
buf[ 4999 ] = '\0';
printf("Select callback: Last piece: %s\n", buf);
}

/* -------------------------------------------------------------- */
/* Fetch callback to specify buffers. */
/* -------------------------------------------------------------- */
static sb4 fetch_cbk(dvoid *ctxp, OCIDefine *dfnhp, ub4 iter, dvoid **bufpp,
ub4 **alenpp, ub1 *piecep, dvoid **indpp, ub2 **rcpp)
{
static int a = 0;
ub4 outpos = *((ub4 *)ctxp);
ub4 len = 5000;
switch(outpos)
{
case 1:
a ++;
*bufpp = (dvoid *) buf;
*alenpp = &len;
break;
default:
*bufpp = (dvoid *) 0;
*alenpp = (ub4 *) 0;
printf("ERROR: invalid position number: %d\n", outpos);
}
*indpp = (dvoid *) 0;
*rcpp = (ub2 *) 0;

buf[len] = '\0';
if (a<=1)
{
*piecep = OCI_FIRST_PIECE;
printf("Select callback: 0th piece\n");
}
else if (a<3)
{
*piecep = OCI_NEXT_PIECE;
printf("Select callback: %d'th piece: %s\n", a-1, buf);
}
else {
*piecep = OCI_LAST_PIECE;
printf("Select callback: %d'th piece: %s\n", a-1, buf);
a = 0;
}
return OCI_CONTINUE;
}

Selecting a LOB Column into a LONG Buffer Using an Array Fetch

The following example illustrates selecting a LOB column into a LONG buffer using an array fetch:

void array_fetch()
{
word i;
text arrbuf[5][5000];
text *selstmt = (text *) "SELECT Ad_sourcetext FROM Print_media WHERE\
Product_id = 2004 AND Ad_id >=4";

OCIStmtPrepare(stmthp, errhp, selstmt, (ub4)strlen((char *)selstmt),
(ub4) OCI_NTV_SYNTAX, (ub4) OCI_DEFAULT);

OCIStmtExecute(svchp, stmthp, errhp, (ub4) 0, (ub4) 0,
(const OCISnapshot*) 0, (OCISnapshot*) 0, (ub4) OCI_DEFAULT);

OCIDefineByPos(stmthp, &defhp1, errhp, (ub4) 1,
(dvoid *) arrbuf[0], (sb4) sizeof(arrbuf[0]),
(ub2) SQLT_CHR, (dvoid *) 0,
(ub2 *) 0, (ub2 *) 0, (ub4) OCI_DEFAULT);

OCIDefineArrayOfStruct(dfnhp1, errhp, sizeof(arrbuf[0]), indsk,
rlsk, rcsk);

retval = OCIStmtFetch(stmthp, errhp, (ub4) 5,
(ub4) OCI_FETCH_NEXT, (ub4) OCI_DEFAULT);
if (retval == OCI_SUCCESS || retval == OCI_SUCCESS_WITH_INFO)
{
printf("%.5000s\n", arrbuf[0]);
printf("%.5000s\n", arrbuf[1]);
printf("%.5000s\n", arrbuf[2]);
printf("%.5000s\n", arrbuf[3]);
printf("%.5000s\n", arrbuf[4]);
}
}

Using the Data Interface for Persistent LOBs in Java

You can also read and write CLOB and BLOB data using the same streaming mechanism as for LONG and LONG RAW data. To read, use defineColumnType(nn, Types.LONGVARCHAR) or defineColumnType(nn, Types.LONGVARBINARY) on the column. This produces a direct stream on the data as if it is a LONG or LONG RAW column. For input in a PreparedStatement, you may use setBinaryStream(), setCharacterStream(), or setAsciiStream() for a parameter which is a BLOB or CLOB. These methods use the stream interface to create a LOB in the database from the data in the stream. Both of these techniques reduce database round trips and may result in improved performance in some cases. See the Javadoc on stream data for the significant restrictions which apply, at http://www.oracle.com/technology/index.html.

Refer to the following in the JDBC Developer's Guide and Reference:

See Also:

- Oracle Database JDBC Developer's Guide and Reference, chapter 14, "Working with LOBs and BFILEs", section "Shortcuts for Inserting and Retrieving CLOB Data"

- Oracle Database JDBC Developer's Guide and Reference, chapter 5, "JDBC Standards Support"

Using the Data Interface with Remote LOBs

The data interface for insert, update, and select of remote LOBs (access over a dblink) is supported since Oracle Database 10g Release 2. The examples in the following sections are for the print_media table created in two schemas: dbs1 and dbs2. The CLOB column of that table used in the examples shown is ad_finaltext. The examples to be given for PL/SQL, OCI, and Java use binds and defines for this one column, but multiple columns can also be accessed. Here is the functionality supported and its limitations:

- You can define a CLOB as CHAR or NCHAR and an NCLOB as CHAR or NCHAR. CLOB and NCLOB can be defined as a LONG. A BLOB can be defined as a RAW or a LONG RAW.

- Queries involving more than one database are not supported:

SELECT t1.lobcol, a2.lobcol FROM t1, t2.lobcol@dbs2 a2 WHERE
LENGTH(t1.lobcol) = LENGTH(a2.lobcol);

Neither is this query:

SELECT t1.lobcol FROM t1@dbs1
UNION ALL
SELECT t2.lobcol FROM t2@dbs2;

- DDL commands are not supported, so the following returns an error:

CREATE VIEW v AS SELECT lob_col FROM tab@dbs;

- Only binds and defines for data going into remote persistent LOBs are supported, so that parameter passing in PL/SQL where CHAR data is bound or defined for remote LOBs is not allowed. These statements all produce errors:

SELECT foo() FROM table1@dbs2;

SELECT foo()@dbs INTO char_val FROM DUAL;

SELECT XMLType().getclobval FROM table1@dbs2;

- If the remote object is a view such as

CREATE VIEW v AS SELECT foo() FROM ...
/* The local database then tries to get the CLOB data and has an error */
SELECT * FROM v@dbs2;

- RETURNING INTO does not support implicit conversions between CHAR and CLOB.

- PL/SQL parameter passing is not allowed where the actual argument is a LOB type and the remote argument is a VARCHAR2, NVARCHAR2, CHAR, NCHAR, or RAW.

- Array binds and defines are supported.

Remote Data Interface Example in PL/SQL

The data interface only supports data of size less than 32KB in PL/SQL. The following snippet shows a PL/SQL example:

CONNECT pm/pm
declare
my_ad varchar(6000) := lpad('b', 6000, 'b');
BEGIN
INSERT INTO print_media@dbs2(product_id, ad_id, ad_finaltext)
VALUES (10000, 10, my_ad);
-- Reset the buffer value
my_ad := 'a';
SELECT ad_finaltext INTO my_ad FROM print_media@dbs2
WHERE product_id = 10000;
END;
/

If ad_finaltext were a BLOB column instead of a CLOB, my_ad has to be of type RAW. If the LOB is greater than 32KB - 1 in size, then PL/SQL will raise a truncation error and the contents of the buffer are undefined.

Remote Data Interface Example in OCI

The data interface only supports data of size less than 2 GB (the maximum value possible of a variable declared as sb4) for OCI. The following pseudocode can be enhanced to be a part of an OCI program:

...
text *sql = (text *)"insert into print_media@dbs2
(product_id, ad_id, ad_finaltext)
values (:1, :2, :3)";
OCIStmtPrepare(...);
OCIBindByPos(...); /* Bind data for positions 1 and 2
* which are independent of LOB */
OCIBindByPos(stmthp, &bndhp[2], errhp, (ub4) 3,
(dvoid *) charbuf1, (sb4) len_charbuf1, SQLT_CHR,
(dvoid *) 0, (ub2 *)0, (ub2 *)0, 0, 0, OCI_DEFAULT);
OCIStmtExecute(...);

...

text *sql = (text *)"select ad_finaltext from print_media@dbs2
where product_id = 10000";
OCIStmtPrepare(...);
OCIDefineByPos(stmthp, &dfnhp[2], errhp, (ub4) 1,
(dvoid *) charbuf2, (sb4) len_charbuf2, SQLT_CHR,
(dvoid *) 0, (ub2 *)0, (ub2 *)0, OCI_DEFAULT);
OCIStmtExecute(...);
...

If ad_finaltext were a BLOB instead of a CLOB, then you bind and define using type SQLT_BIN. If the LOB is greater than 2GB - 1 in size, then OCI will raise a truncation error and the contents of the buffer are undefined.

Remote Data Interface Examples in JDBC

The following code snippets works with all three JDBC drivers (OCI, Thin, and kprb in the database):

Bind:

This is for the non-streaming mode:

...
String sql = "insert into print_media@dbs2 (product_id, ad_id, ad_final_text)" +
" values (:1, :2, :3)";
PreparedStatement pstmt = conn.prepareStatement(sql);
pstmt.setInt( 1, 2 );
pstmt.setInt( 2, 20);
pstmt.setString( 3, "Java string" );
int rows = pstmt.executeUpdate();
...

For the streaming mode, the same code as the preceding works, except that the setString() statement is replaced by one of the following:

pstmt.setCharacterStream( 3, new LabeledReader(), 1000000 );
pstmt.setAsciiStream( 3, new LabeledAsciiInputStream(), 1000000 );

Here, LabeledReader() and LabeledAsciiInputStream() produce character and ASCII streams respectively. If ad_finaltext were a BLOB column instead of a CLOB, then the preceding example works if the bind is of type RAW:

pstmt.setBytes( 3, <some byte[] array> );

pstmt.setBinaryStream( 3, new LabeledInputStream(), 1000000 );

Here, LabeledInputStream() produces a binary stream.

Define:

For non-streaming mode:

OracleStatement stmt = (OracleStatement)(conn.createStatement());
stmt.defineColumnType( 1, Types.VARCHAR );
ResultSet rst = stmt.executeQuery("select ad_finaltext from print_media@dbs2" );
while( rst.next() )
{
String s = rst.getString( 1 );
System.out.println( s );
}

For streaming mode:

OracleStatement stmt = (OracleStatement)(conn.createStatement());
stmt.defineColumnType( 1, Types.LONGVARCHAR );
ResultSet rst = stmt.executeQuery("select ad_finaltext from print_media@dbs2" );
while( rst.next() )
{
Reader reader = rst.getCharacterStream( 1 );
while( reader.ready() )
{
System.out.print( (char)(reader.next()) );
}
System.out.println();
}

If ad_finaltext were a BLOB column instead of a CLOB, then the preceding examples work if the define is of type RAW:

stmt.defineColumnType( 1, Types.RAW ) // or LONGRAW
...
String s = rst.getBytes( 1 );
Reader reader = rst.getBinaryStream( 1 );

See Also:

Oracle Database JDBC Developer's Guide and Reference, chapter 14, "Working with LOBs and BFILEs", section "Shortcuts for Inserting and Retrieving CLOB Data"

14 LOB APIs for Basic Operations

This chapter describes APIs that perform basic operations on BLOB, CLOB, and NCLOB datatypes. The operations given in this chapter can be used with either persistent or temporary LOB instances. Note that operations in this chapter do not apply to BFILEs. APIs covered in this chapter are listed in Table 14-1.

See Also:

- Chapter 12, "Operations Specific to Persistent and Temporary LOBs" for information on how to create temporary and persistent LOB instances and other operations specific to temporary or persistent LOBs.

- Chapter 15, "LOB APIs for BFILE Operations" for information on operations specific to BFILE instances.

The following information is given for each operation described in this chapter:

- Preconditions describe dependencies that must be met and conditions that must exist before calling each operation.

- Usage Notes provide implementation guidelines such as information specific to a given programmatic environment or datatype.

- Syntax refers you to the syntax reference documentation for each supported programmatic environment.

- Examples describe any setup tasks necessary to run the examples given. Demonstration files listed are available in subdirectories under $ORACLE_HOME/rdbms/demo/lobs/ named plsql, oci, vb, and java. The driver program lobdemo.sql is in /plsql and the driver program lobdemo.c is in /oci.

This chapter contains these topics:

- Supported Environments

- Appending One LOB to Another

- Determining Character Set Form

- Determining Character Set ID

- Loading a LOB with Data from a BFILE

- Loading a BLOB with Data from a BFILE

- Loading a CLOB or NCLOB with Data from a BFILE

- Determining Whether a LOB is Open

- Displaying LOB Data

- Reading Data from a LOB

- LOB Array Read

- Reading a Portion of a LOB (SUBSTR)

- Comparing All or Part of Two LOBs

- Patterns: Checking for Patterns in a LOB Using INSTR

- Length: Determining the Length of a LOB

- Copying All or Part of One LOB to Another LOB

- Copying a LOB Locator

- Equality: Checking If One LOB Locator Is Equal to Another

- Determining Whether LOB Locator Is Initialized

- Appending to a LOB

- Writing Data to a LOB

- LOB Array Write

- Trimming LOB Data

- Erasing Part of a LOB

- Enabling LOB Buffering

- Flushing the Buffer

- Disabling LOB Buffering

- Determining Whether a LOB instance Is Temporary

- Converting a BLOB to a CLOB

- Converting a CLOB to a BLOB

Supported Environments

Table 14-1, "Environments Supported for Basic LOB APIs" indicates which programmatic environments are supported for the APIs discussed in this chapter. The first column describes the operation that the API performs. The remaining columns indicate with "Yes" or "No" whether the API is supported in PL/SQL, OCI, OCCI, COBOL, Pro*C/C++, Visual Basic (VB), and JDBC.

Table 14-1 Environments Supported for Basic LOB APIs

Operation

PL/SQL

OCI

OCCI

COBOL

Pro*C/C++

VB

JDBC

Appending One LOB to Another

Yes

Yes

No

Yes

Yes

Yes

Yes

Determining Character Set Form

No

Yes

No

No

No

No

No

Determining Character Set ID

No

Yes

No

No

No

No

No

Determining Chunk Size, See: Writing Data to a LOB

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Comparing All or Part of Two LOBs

Yes

No

No

Yes

Yes

Yes

Yes

Converting a BLOB to a CLOB

Yes

No

No

No

No

No

No

Converting a CLOB to a BLOB

Yes

No

No

No

No

No

No

Copying a LOB Locator

Yes

Yes

No

Yes

Yes

Yes

Yes

Copying All or Part of One LOB to Another LOB

Yes

Yes

No

Yes

Yes

Yes

Yes

Disabling LOB Buffering

No

Yes

No

Yes

Yes

Yes

No

Displaying LOB Data

Yes

Yes

No

Yes

Yes

Yes

Yes

Enabling LOB Buffering

No

No

No

Yes

Yes

Yes

No

Equality: Checking If One LOB Locator Is Equal to Another

No

Yes

No

No

Yes

No

Yes

Erasing Part of a LOB

Yes

Yes

No

Yes

Yes

Yes

Yes

Flushing the Buffer

No

Yes

No

Yes

Yes

No

No

Determining Whether LOB Locator Is Initialized

No

Yes

No

No

Yes

No

No

Length: Determining the Length of a LOB

Yes

Yes

No

Yes

Yes

Yes

Yes

Loading a LOB with Data from a BFILE

Yes

Yes

No

Yes

Yes

Yes

Yes

Loading a BLOB with Data from a BFILE

Yes

No

No

No

No

No

No

Loading a CLOB or NCLOB with Data from a BFILE

Yes

No

No

No

No

No

No

LOB Array Read

No

Yes

No

No

No

No

No

LOB Array Write

No

Yes

No

No

No

No

No

Opening Persistent LOBs with the OPEN and CLOSE Interfaces

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Open: Determining Whether a LOB is Open

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Patterns: Checking for Patterns in a LOB Using INSTR

Yes

No

No

Yes

Yes

No

Yes

Reading a Portion of a LOB (SUBSTR)

Yes

No

No

Yes

Yes

Yes

Yes

Reading Data from a LOB

Yes

Yes

No

Yes

Yes

Yes

Yes

Storage Limit, Determining: Maximum Storage Limit for Terabyte-Size LOBs

Yes

No

No

No

No

No

No

Trimming LOB Data

Yes

Yes

No

Yes

Yes

Yes

Yes

WriteNoAppend, see Appending to a LOB .

No

No

No

No

No

No

No

Writing Data to a LOB

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Appending One LOB to Another

This operation appends one LOB instance to another.

Preconditions

Before you can append one LOB to another, the following conditions must be met:

- Two LOB instances must exist.

- Both instances must be of the same type, for example both BLOB or both CLOB types.

- You can pass any combination of persistent or temporary LOB instances to this operation.

Usage Notes

Persistent LOBs: You must lock the row you are selecting the LOB from prior to updating a LOB value if you are using the PL/SQL DBMS_LOB Package or OCI. While the SQL INSERT and UPDATE statements implicitly lock the row, locking the row can be done explicitly using the SQL SELECT FOR UPDATE statement in SQL and PL/SQL programs, or by using an OCI pin or lock function in OCI programs. For more details on the state of the locator after an update, refer to "Example of Updating LOBs Through Updated Locators".

Syntax

See the following syntax references for each programmatic environment:

- PL/SQL (DBM_LOB Package): Oracle Database PL/SQL Packages and Types Reference "DBMS_LOB" — APPEND

- C (OCI): Oracle Call Interface Programmer's Guide "LOB Functions" — OCILobAppend()

- C++ (OCCI): Oracle C++ Call Interface Programmer's Guide

- COBOL (Pro*COBOL) Pro*COBOL Programmer's Guide for information on LOBs, usage notes on LOB Statements, and embedded SQL and precompiler directives — LOB APPEND.

- C/C++ (Pro*C/C++): Pro*C/C++ Programmer's Guide for information on embedded SQL statements and directives — LOB APPEND

- Visual Basic (OO4O): (Oracle Objects for OLE (OO4O) Online Help): From Help Topics, Contents tab, select OO4O Automation Server > OBJECTS > Orablob > METHODS > append

- Java (JDBC): Oracle Database JDBC Developer's Guide and Reference for information on creating and populating LOB columns in Java.

Examples

To run the following examples, you must create two LOB instances and pass them when you call the given append operation. Creating a LOB instance is described in Chapter 12, "Operations Specific to Persistent and Temporary LOBs".

Examples for this use case are provided in the following programmatic environments:

- PL/SQL (DBMS_LOB Package): lappend.sql

- OCI: lappend.c

- Visual Basic (OO4O): lappend.bas

- Java (JDBC): lappend.java

Determining Character Set Form

This section describes how to get the character set form of a LOB instance.

Syntax

Use the following syntax references for each programmatic environment:

- PL/SQL (DBMS_LOB Package): There is no applicable syntax reference for this operation.

- C (OCI): Oracle Call Interface Programmer's Guide "LOB Functions" — OCILobCharSetForm()

- C++ (OCCI): Oracle C++ Call Interface Programmer's Guide

- COBOL (Pro*COBOL): There is no applicable syntax reference for this operation

- C/C++ (Pro*C/C++): There is no applicable syntax reference for this operation.

- Visual Basic (OO4O): There is no applicable syntax reference for this operation.

- Java (JDBC): There is no applicable syntax reference for this operation.

Example

The example demonstrates how to determine the character set form of the foreign language text (ad_fltextn).

This functionality is currently available only in OCI:

- OCI: lgetchfm.c

Determining Character Set ID

This section describes how to determine the character set ID.

Syntax

Use the following syntax references for each programmatic environment:

- PL/SQL (DBMS_LOB Package): There is no applicable syntax reference for this operation.

- C (OCI): Oracle Call Interface Programmer's Guide "Relational Functions" — LOB Functions, OCILobCharSetId()

- C++ (OCCI): Oracle C++ Call Interface Programmer's Guide

- COBOL (Pro*COBOL): There is no applicable syntax reference for this operation.

- C/C++ (Pro*C/C++): There is no applicable syntax reference for this operation

- Visual Basic (OO4O): There is no applicable syntax reference for this operation.

- Java (JDBC): There is no applicable syntax reference for this operation.

Example

This functionality is currently available only in OCI:

- OCI: lgetchar.c

Loading a LOB with Data from a BFILE

This operation loads a LOB with data from a BFILE. This procedure can be used to load data into any persistent or temporary LOB instance of any LOB datatype.

See Also:

- The LOADBLOBFROMFILE and LOADCLOBFROMFILE procedures implement the functionality of this procedure and provide improved features for loading binary data and character data. (These improved procedures are available in the PL/SQL environment only.) When possible, using one of the improved procedures is recommended. See "Loading a BLOB with Data from a BFILE" and "Loading a CLOB or NCLOB with Data from a BFILE" for more information.

- As an alternative to this operation, you can use SQL*Loader to load persistent LOBs with data directly from a file in the file system. See "Using SQL*Loader to Load LOBs" for more information.

Preconditions

Before you can load a LOB with data from a BFILE, the following conditions must be met:

- The BFILE must exist.

- The target LOB instance must exist.

Usage Notes

Note the following issues regarding this operation.

Use LOADCLOBFROMFILE When Loading Character Data

When you use the DBMS_LOB.LOADFROMFILE procedure to load a CLOB or NCLOB instance, you are loading the LOB with binary data from the BFILE and no implicit character set conversion is performed. For this reason, using the DBMS_LOB.LOADCLOBFROMFILE procedure is recommended when loading character data, see Loading a CLOB or NCLOB with Data from a BFILE on for more information.

Specifying Amount of BFILE Data to Load

The value you pass for the amount parameter to functions listed in Table 14-2 must be one of the following:

- An amount less than or equal to the actual size (in bytes) of the BFILE you are loading.

- The maximum allowable LOB size (in bytes). Passing this value, loads the entire BFILE. You can use this technique to load the entire BFILE without determining the size of the BFILE before loading. To get the maximum allowable LOB size, use the technique described in Table 14-2.

Table 14-2 Maximum LOB Size for Load from File Operations

Environment

Function

To pass maximum LOB size, get value of:

DBMS_LOB

DBMS_LOB.LOADBLOBFROMFILE

DBMS_LOB.LOBMAXSIZE

DBMS_LOB

DBMS_LOB.LOADCLOBFROMFILE

DBMS_LOB.LOBMAXSIZE

OCI

OCILobLoadFromFile2()

(For LOBs of any size.)

UB8MAXVAL

OCI

OCILobLoadFromFile()

(For LOBs less than 4 gigabytes in size.)

UB4MAXVAL

Syntax

See the following syntax references for details on using this operation in each programmatic environment:

- PL/SQL (DBMS_LOB Package): Oracle Database PL/SQL Packages and Types Reference "DBMS_LOB" — LOADFROMFILE.

- C (OCI): Oracle Call Interface Programmer's Guide "LOB Functions" — OCILobLoadFromFile().

- C++ (OCCI): Oracle C++ Call Interface Programmer's Guide

- COBOL (Pro*COBOL) Pro*COBOL Programmer's Guide for information on LOBs, usage notes on LOB statements, and embedded SQL and precompiler directives — LOB LOAD, LOB OPEN, LOB CLOSE.

- C/C++ (Pro*C/C++): Pro*C/C++ Programmer's Guide Appendix F, "Embedded SQL Statements and Directives" — LOB LOAD

- Visual Basic (OO4O) (Oracle Objects for OLE (OO4O) Online Help): From help Topics, Contents tab, select OO4O Automation Server > OBJECTS > OraBfile > METHODS > CopyFromBFILE and select OO4O Automation Server > OBJECTS > OraDynaset, OraDatabase, OraConnection

- Java (JDBC): Oracle Database JDBC Developer's Guide and Reference Chapter 7, "Working With LOBs" — Creating and Populating a BLOB or CLOB Column.

Examples

Examples are provided in the following programmatic environments:

- PL/SQL (DBMS_LOB Package): lloaddat.sql

- OCI: lloaddat.c

- Visual Basic (OO4O): lloaddat.bas

- Java (JDBC): lloaddat.java

Loading a BLOB with Data from a BFILE

This procedure loads a BLOB with data from a BFILE. This procedure can be used to load data into any persistent or temporary BLOB instance.

See Also:

- "Loading a LOB with Data from a BFILE"

- To load character data, use DBMS_LOB.LOADCLOBFROMFILE. See "Loading a CLOB or NCLOB with Data from a BFILE" for more information.

- As an alternative to this operation, you can use SQL*Loader to load persistent LOBs with data directly from a file in the file system. See "Using SQL*Loader to Load LOBs" for more information.

Preconditions

The following conditions must be met before calling this procedure:

- The target BLOB instance must exist.

- The source BFILE must exist.

- You must open the BFILE. (After calling this procedure, you must close the BFILE at some point.)

Usage Notes

Note the following with respect to this operation:

New Offsets Returned

Using DBMS_LOB.LOADBLOBFROMFILE to load binary data into a BLOB achieves the same result as using DBMS_LOB.LOADFROMFILE, but also returns the new offsets of BLOB.

Specifying Amount of BFILE Data to Load

The value you pass for the amount parameter to the DBMS_LOB.LOADBLOBFROMFILE function must be one of the following:

- An amount less than or equal to the actual size (in bytes) of the BFILE you are loading.

- The maximum allowable LOB size: DBMS_LOB.LOBMAXSIZE. Passing this value causes the function to load the entire BFILE. This is a useful technique for loading the entire BFILE without introspecting the size of the BFILE.

See Also:

Table 14-2, "Maximum LOB Size for Load from File Operations"

Syntax

See Oracle Database PL/SQL Packages and Types Reference, "DBMS_LOB" — LOADBLOBFROMFILE procedure for syntax details on this procedure.

Examples

This example is available in PL/SQL only. This API is not provided in other programmatic environments. The online file is lldblobf.sql. This example illustrates:

- How to use LOADBLOBFROMFILE to load the entire BFILE without getting its length first.

- How to use the return value of the offsets to calculate the actual amount loaded.

Loading a CLOB or NCLOB with Data from a BFILE

This procedure loads a CLOB or NCLOB with character data from a BFILE. This procedure can be used to load data into a persistent or temporary CLOB or NCLOB instance.

See Also:

- "Loading a LOB with Data from a BFILE"

- To load binary data, use DBMS_LOB.LOADBLOBFROMFILE. See "Loading a BLOB with Data from a BFILE" for more information.

- As an alternative to this operation, you can use SQL*Loader to load persistent LOBs with data directly from a file in the file system. See "Using SQL*Loader to Load LOBs" for more information.

Preconditions

The following conditions must be met before calling this procedure:

- The target CLOB or NCLOB instance must exist.

- The source BFILE must exist.

- You must open the BFILE. (After calling this procedure, you must close the BFILE at some point.)

Usage Notes

You can specify the character set id of the BFILE when calling this procedure. Doing so, ensures that the character set is properly converted from the BFILE data character set to the destination CLOB or NCLOB character set.

Specifying Amount of BFILE Data to Load

The value you pass for the amount parameter to the DBMS_LOB.LOADCLOBFROMFILE function must be one of the following:

- An amount less than or equal to the actual size (in characters) of the BFILE data you are loading.

- The maximum allowable LOB size: DBMS_LOB.LOBMAXSIZE

Passing this value causes the function to load the entire BFILE. This is a useful technique for loading the entire BFILE without introspecting the size of the BFILE.

Syntax

See Oracle Database PL/SQL Packages and Types Reference, "DBMS_LOB" — LOADCLOBFROMFILE procedure for syntax details on this procedure.

Examples

The following examples illustrate different techniques for using this API:

- "PL/SQL: Loading Character Data from a BFILE into a LOB"

- "PL/SQL: Loading Segments of Character Data into Different LOBs"

PL/SQL: Loading Character Data from a BFILE into a LOB

The following example illustrates:

- How to use default csid (0).

- How to load the entire file without calling getlength for the BFILE.

- How to find out the actual amount loaded using return offsets.

This example assumes that ad_source is a BFILE in UTF8 character set format and the database character set is UTF8. The online file is lldclobf.sql.

PL/SQL: Loading Segments of Character Data into Different LOBs

The following example illustrates:

- How to get the character set ID from the character set name using the NLS_CHARSET_ID function.

- How to load a stream of data from a single BFILE into different LOBs using the returned offset value and the language context lang_ctx.

- How to read a warning message.

This example assumes that ad_file_ext_01 is a BFILE in JA16TSTSET format and the database national character set is AL16UTF16. The online file is lldclobs.sql.

Determining Whether a LOB is Open

This operation determines whether a LOB is open.

Preconditions

The LOB instance must exist before executing this procedure.

Usage Notes

When a LOB is open, it must be closed at some point later in the session.

Syntax

Use the following syntax references for each programmatic environment:

- PL/SQL (DBMS_LOB Package): Oracle Database PL/SQL Packages and Types Reference "DBMS_LOB" — OPEN, ISOPEN.

- C (OCI): Oracle Call Interface Programmer's Guide "LOB Functions" — OCILobIsOpen().

- C++ (OCCI): Oracle C++ Call Interface Programmer's Guide

- COBOL (Pro*COBOL) Pro*COBOL Programmer's Guide for information on LOBs, usage notes on LOB Statements, and embedded SQL and precompiler directives — LOB DESCRIBE.

- C/C++ (Pro*C/C++): Pro*C/C++ Programmer's Guide Appendix F, "Embedded SQL Statements and Directives" — LOB DESCRIBE ... ISOPEN ...

- Visual Basic (OO4O): There is no applicable syntax reference for this use case.

- Java (JDBC): Oracle Database JDBC Developer's Guide and Reference, "Working With LOBs" — Creating and Populating a BLOB or CLOB Column.

Examples

Examples are provided in the following programmatic environments:

- PL/SQL (DBMS_LOB Package): lisopen.sql

- OCI: lisopen.c

- C++ (OCCI): No example is provided with this release.

- Visual Basic (OO4O): No example is provided with this release.

- Java (JDBC): lisopen.java

Java (JDBC): Checking If a LOB Is Open

Here is how to check a BLOB or a CLOB.

Checking If a CLOB Is Open

To see if a CLOB is open, your JDBC application can use the isOpen method defined in oracle.sql.CLOB. The return Boolean value indicates whether the CLOB has been previously opened or not. The isOpen method is defined as follows:

/**
* Check whether the CLOB is opened.
* @return true if the LOB is opened.
*/
public boolean isOpen () throws SQLException

The usage example is:

CLOB clob = ...
// See if the CLOB is opened
boolean isOpen = clob.isOpen ();
...

Checking If a BLOB Is Open

To see if a BLOB is open, your JDBC application can use the isOpen method defined in oracle.sql.BLOB. The return Boolean value indicates whether the BLOB has been previously opened or not. The isOpen method is defined as follows:

/**
* Check whether the BLOB is opened.
* @return true if the LOB is opened.
*/
public boolean isOpen () throws SQLException

The usage example is:

BLOB blob = ...
// See if the BLOB is opened
boolean isOpen = blob.isOpen ();
...

Displaying LOB Data

This section describes APIs that allow you to read LOB data. You can use this operation to read LOB data into a buffer. This is useful if your application requires displaying large amounts of LOB data or streaming data operations.

Usage Notes

Note the following when using these APIs.

Streaming Mechanism

The most efficient way to read large amounts of LOB data is to use OCILobRead2() with the streaming mechanism enabled.

Amount Parameter

The value you pass for the amount parameter is restricted for the APIs described in Table 14-3.

Table 14-3 Maximum LOB Size for Amount Parameter

Environment

Function

Value of amount parameter is limited to:

DBMS_LOB

DBMS_LOB.READ

The size of the buffer, 32Kbytes.

OCI

OCILobRead()

(For LOBs less than 4 gigabytes in size.)

UB4MAXVAL

Specifying this amount reads the entire file.

OCI

OCILobRead2()

(For LOBs of any size.)

UB8MAXVAL

Specifying this amount reads the entire file.

Syntax

Use the following syntax references for each programmatic environment:

- PL/SQL (DBM_LOB Package): Oracle Database PL/SQL Packages and Types Reference "DBMS_LOB" — OPEN, READ, CLOSE.

- C (OCI): Oracle Call Interface Programmer's Guide "LOB Functions" —, OCILobOpen(), OCILobRead2(), OCILobClose().

- C++ (OCCI): Oracle C++ Call Interface Programmer's Guide

- COBOL (Pro*COBOL) Pro*COBOL Programmer's Guide for information on LOBs, usage notes on LOB statements, and embedded SQL and precompiler directives — LOB READ.

- C/C++ (Pro*C/C++): Pro*C/C++ Programmer's Guide Appendix F, "Embedded SQL Statements and Directives" — LOB READ

- Visual Basic (OO4O) (Oracle Objects for OLE (OO4O) Online Help): From Help Topics, Contents tab, select OO4O Automation Server > OBJECTS > Oraclob > METHODS > read, and > OBJECTS > Oraclob > PROPERTIES > offset

- Java (JDBC): Oracle Database JDBC Developer's Guide and Reference, "Working With LOBs" — Creating and Populating a BLOB or CLOB Column.

Examples

Examples are provided in the following programmatic environments:

- PL/SQL (DBMS_LOB Package): ldisplay.sql

- OCI: ldisplay.c

- C++ (OCCI): No example is provided in this release.

- Visual Basic (OO4O): ldisplay.bas

- Java (JDBC): ldisplay.java

Reading Data from a LOB

This section describes how to read data from LOBs using OCILobRead2().

Usage Notes

Note the following when using this operation.

Streaming Read in OCI

The most efficient way to read large amounts of LOB data is to use OCILobRead2() with the streaming mechanism enabled using polling or callback. To do so, specify the starting point of the read using the offset parameter as follows:

ub8  char_amt =  0;
ub8  byte_amt =  0;
ub4  offset = 1000;

OCILobRead2(svchp, errhp, locp, &byte_amt, &char_amt, offset, bufp, bufl,
OCI_ONE_PIECE, 0, 0, 0, 0);

When using polling mode, be sure to look at the value of the byte_amt parameter after each OCILobRead2() call to see how many bytes were read into the buffer because the buffer may not be entirely full.

When using callbacks, the lenp parameter, which is input to the callback, will indicate how many bytes are filled in the buffer. Be sure to check the lenp parameter during your callback processing because the entire buffer may not be filled with data (see the Oracle Call Interface Programmer's Guide.)

Chunk Size

A chunk is one or more Oracle blocks. You can specify the chunk size for the LOB when creating the table that contains the LOB. This corresponds to the data size used by Oracle Database when accessing or modifying the LOB value. Part of the chunk is used to store system-related information and the rest stores the LOB value. The API you are using has a function that returns the amount of space used in the LOB chunk to store the LOB value. In PL/SQL use DBMS_LOB.GETCHUNKSIZE. In OCI, use OCILobGetChunkSize().

You will improve performance if you run write requests using a multiple of the value returned by one of these functions. The reason for this is that you are using the same unit that the Oracle database uses when reading data from disk. If it is appropriate for your application, then you should batch reads until you have enough for an entire chunk instead of issuing several LOB read calls that operate on the same LOB chunk.

Syntax

Use the following syntax references for each programmatic environment:

- PL/SQL (DBM_LOB Package): Oracle Database PL/SQL Packages and Types Reference "DBMS_LOB" — OPEN, GETCHUNKSIZE, READ, CLOSE.

- C (OCI): Oracle Call Interface Programmer's Guide "LOB Functions" — OCILobOpen(), OCILobRead2(), OCILobClose().

- C++ (OCCI): Oracle C++ Call Interface Programmer's Guide

- COBOL (Pro*COBOL) Pro*COBOL Programmer's Guide for information on LOBs, usage notes on LOB statements, and embedded SQL and precompiler directives — LOB READ.

- C/C++ (Pro*C/C++): Pro*C/C++ Programmer's Guide Appendix F, "Embedded SQL Statements and Directives" — LOB READ

- Visual Basic (OO4O) (Oracle Objects for OLE (OO4O) Online Help): From Help Topics, Contents tab, select OO4O Automation Server > OBJECTS > Oraclob > METHODS > read

- Java (JDBC): Oracle Database JDBC Developer's Guide and Reference Chapter 7, "Working With LOBs" — Creating and Populating a BLOB or CLOB Column.

Examples

Examples are provided in the following programmatic environments:

- PL/SQL (DBMS_LOB Package): lread.sql

- OCI: lread.c

- Visual Basic (OO4O): lread.bas

- Java (JDBC): lread.java

LOB Array Read

This section describes how to read LOB data for multiple locators in one round trip, using OCILobArrayRead().

Usage Notes

This function improves performance in reading LOBs in the size range less than about 512 Kbytes. For an OCI application example, assume that the program has a prepared SQL statement such as:

SELECT lob1 FROM lob_table for UPDATE;

where lob1 is the LOB column and lob_array is an array of define variables corresponding to a LOB column:

OCILobLocator * lob_array[10];

...
for (i=0; i<10, i++)        /* initialize array of locators */
lob_array[i] = OCIDescriptorAlloc(..., OCI_DTYPE_LOB, ...);

...

OCIDefineByPos(..., 1, (dvoid *) lob_array, ... SQLT_CLOB, ...);

/* Execute the statement with iters = 10 to do an array fetch of 10 locators. */
OCIStmtExecute ( <service context>, <statement handle>, <error handle>,
10,    /* iters  */
0,     /* row offset */
NULL,  /* snapshot IN */
NULL,  /* snapshot out */
OCI_DEFAULT /* mode */);
...

ub4 array_iter = 10;
char  *bufp[10];
oraub8 bufl[10];
oraub8 char_amtp[10];
oraub8 offset[10];

for (i=0; i<10; i++)
{
bufp[i] = (char *)malloc(1000);
bufl[i] = 1000;
offset[i] = 1;
char_amtp[i] = 1000;  /* Single byte fixed width char set. */
}

/* Read the 1st 1000 characters for all 10 locators in one
* round trip. Note that offset and amount need not be
* same for all the locators. */

OCILobArrayRead(<service context>, <error handle>,
&array_iter, /* array size */
lob_array,   /* array of locators */
NULL,        /* array of byte amounts */
char_amtp,   /* array of char amounts */
offset,      /* array of offsets */
(void **)bufp,        /* array of read buffers */
bufl,        /* array of buffer lengths */
OCI_ONE_PIECE,  /* piece information */
NULL,           /* callback context */
NULL,           /* callback function */
0,              /* character set ID - default */
SQLCS_IMPLICIT);/* character set form */

...

for (i=0; i<10; i++)
{
/* Fill bufp[i] buffers with data to be written */
strncpy (bufp[i], "Test Data------", 15);
bufl[i] = 1000;
offset[i] = 50;
char_amtp[i] = 15;  /* Single byte fixed width char set. */
}

/* Write the 15 characters from offset 50 to all 10
* locators in one round trip. Note that offset and
* amount need not be same for all the locators. */
*/

OCILobArrayWrite(<service context>, <error handle>,
&array_iter, /* array size */
lob_array,   /* array of locators */
NULL,        /* array of byte amounts */
char_amtp,   /* array of char amounts */
offset,      /* array of offsets */
(void **)bufp,    /* array of read buffers */
bufl,        /* array of buffer lengths */
OCI_ONE_PIECE,  /* piece information */
NULL,           /* callback context */
NULL,           /* callback function */
0,              /* character set ID - default */
SQLCS_IMPLICIT);/* character set form */
...

Streaming Support

LOB array APIs can be used to read/write LOB data in multiple pieces. This can be done by using polling method or a callback function.Here data is read/written in multiple pieces sequentially for the array of locators. For polling, the API would return to the application after reading/writing each piece with the array_iter parameter (OUT) indicating the index of the locator for which data is read/written. With a callback, the function is called after reading/writing each piece with array_iter as IN parameter.

Note that:

- It is possible to read/write data for a few of the locators in one piece and read/write data for other locators in multiple pieces. Data is read/written in one piece for locators which have sufficient buffer lengths to accommodate the whole data to be read/written.

- Your application can use different amount value and buffer lengths for each locator.

- Your application can pass zero as the amount value for one or more locators indicating pure streaming for those locators. In the case of reading, LOB data is read to the end for those locators. For writing, data is written until OCI_LAST_PIECE is specified for those locators.

LOB Array Read in Polling Mode

The following example reads 10Kbytes of data for each of 10 locators with 1Kbyte buffer size. Each locator needs 10 pieces to read the complete data. OCILobArrayRead() needs to be called 100 (10*10) times to fetch all the data.First we call OCILobArrayRead() with OCI_FIRST_PIECE as piece parameter. This call returns the first 1K piece for the first locator.Next OCILobArrayRead() is called in a loop until the application finishes reading all the pieces for the locators and returns OCI_SUCCESS. In this example it loops 99 times returning the pieces for the locators sequentially.

/* Fetch the locators */
...

/* array_iter parameter indicates the number of locators in the array read.
* It is an IN parameter for the 1st call in polling and is ignored as IN
* parameter for subsequent calls. As OUT parameter it indicates the locator
* index for which the piece is read.
*/

ub4    array_iter = 10;
char  *bufp[10];
oraub8 bufl[10];
oraub8 char_amtp[10];
oraub8 offset[10];
sword  st;

for (i=0; i<10; i++)
{
bufp[i] = (char *)malloc(1000);
bufl[i] = 1000;
offset[i] = 1;
char_amtp[i] = 10000;       /* Single byte fixed width char set. */
}

st =  OCILobArrayRead(<service context>, <error handle>,
&array_iter, /* array size */
lob_array, /* array of locators */
NULL,      /* array of byte amounts */
char_amtp, /* array of char amounts */
offset,    /* array of offsets */
(void **)bufp,      /* array of read buffers */
bufl,      /* array of buffer lengths */
OCI_FIRST_PIECE, /* piece information */
NULL,           /* callback context */
NULL,           /* callback function */
0,              /* character set ID - default */
SQLCS_IMPLICIT); /* character set form */

/* First piece for the first locator is read here.
* bufp[0]          => Buffer pointer into which data is read.
* char_amtp[0 ]    => Number of characters read in current buffer
*
*/

While ( st == OCI_NEED_DATA)
{
st =  OCILobArrayRead(<service context>, <error handle>,
&array_iter, /* array size */
lob_array, /* array of locators */
NULL,      /* array of byte amounts */
char_amtp, /* array of char amounts */
offset,    /* array of offsets */
(void **)bufp,      /* array of read buffers */
bufl,      /* array of buffer lengths */
OCI_NEXT_PIECE, /* piece information */
NULL,           /* callback context */
NULL,           /* callback function */
0,              /* character set ID - default */
SQLCS_IMPLICIT);

/* array_iter returns the index of the current array element for which
* data is read. for example, aray_iter = 1 implies first locator,
* array_iter = 2 implies second locator and so on.
*
* lob_array[ array_iter - 1]=> Lob locator for which data is read.
* bufp[array_iter - 1]      => Buffer pointer into which data is read.
* char_amtp[array_iter - 1] => Number of characters read in current buffer
*/

...
/* Consume the data here */
...
}

LOB Array Read with Callback

The following example reads 10Kbytes of data for each of 10 locators with 1Kbyte buffer size. Each locator needs 10 pieces to read all the data. The callback function is called 100 (10*10) times to return the pieces sequentially.

/* Fetch the locators */
...
ub4    array_iter = 10;
char  *bufp[10];
oraub8 bufl[10];
oraub8 char_amtp[10];
oraub8 offset[10];
sword  st;

for (i=0; i<10; i++)
{
bufp[i] = (char *)malloc(1000);
bufl[i] = 1000;
offset[i] = 1;
char_amtp[i] = 10000;       /* Single byte fixed width char set. */
}

st =  OCILobArrayRead(<service context>, <error handle>,
&array_iter, /* array size */
lob_array,   /* array of locators */
NULL,        /* array of byte amounts */
char_amtp,   /* array of char amounts */
offset,      /* array of offsets */
(void **)bufp,        /* array of read buffers */
bufl,        /* array of buffer lengths */
OCI_FIRST_PIECE,  /* piece information */
ctx,              /* callback context */
cbk_read_lob,     /* callback function */
0,                /* character set ID - default */
SQLCS_IMPLICIT);
...
/* Callback function for LOB array read. */
sb4 cbk_read_lob(dvoid *ctxp, ub4 array_iter, CONST dvoid *bufxp, oraub8 len,
ub1 piece, dvoid **changed_bufpp, oraub8 *changed_lenp)
{
static ub4 piece_count = 0;
piece_count++;
switch (piece)
{
case OCI_LAST_PIECE:
/*--- buffer processing code goes here ---*/
(void) printf("callback read the %d th piece(last piece) for %dth locator \n\n",
piece_count, array_iter );
piece_count = 0;
break;
case OCI_FIRST_PIECE:
/*--- buffer processing code goes here ---*/
(void) printf("callback read the 1st piece for %dth locator\n",
array_iter);
/* --Optional code to set changed_bufpp and changed_lenp if the buffer needs
to be changed dynamically --*/
break;
case OCI_NEXT_PIECE:
/*--- buffer processing code goes here ---*/
(void) printf("callback read the %d th piece for %dth locator\n",
piece_count, array_iter);
/* --Optional code to set changed_bufpp and changed_lenp if the  buffer
needs to be changed dynamically --*/
break;
default:
(void) printf("callback read error: unkown piece = %d.\n", piece);
return OCI_ERROR;
}
return OCI_CONTINUE;
}
...

Polling LOB Array Read

The next example is polling LOB data in OCILobArrayRead() with variable amtp, bufl, and offset.

/* Fetch the locators */
...

ub4    array_iter = 10;
char  *bufp[10];
oraub8 bufl[10];
oraub8 char_amtp[10];
oraub8 offset[10];
sword  st;

for (i=0; i<10; i++)
{
bufp[i] = (char *)malloc(1000);
bufl[i] = 1000;
offset[i] = 1;
char_amtp[i] = 10000;       /* Single byte fixed width char set. */
}

/* For 3rd locator read data in 500 bytes piece from offset 101. Amount
* is 2000, that is, total number of pieces will be 2000/500 = 4.
*/
offset[2] = 101; bufl[2] = 500; char_amtp[2] = 2000;

/* For 6th locator read data in 100 bytes piece from offset 51. Amount
* is 0 indicating pure polling, that is, data will be read till the end of
* the LOB is reached.
*/
offset[5] = 51;  bufl[5] = 100; char_amtp[5] = 0;

/* For 8th locator read 100 bytes of data in one piece. Note amount
* is less than buffer length indicating single piece read.
*/
offset[7] = 61;  bufl[7] = 200; char_amtp[7] = 100;

st =  OCILobArrayRead(<service context>, <error handle>,
&array_iter, /* array size */
lob_array, /* array of locators */
NULL,      /* array of byte amounts */
char_amtp, /* array of char amounts */
offset,    /* array of offsets */
(void **)bufp,      /* array of read buffers */
bufl,      /* array of buffer lengths */
OCI_FIRST_PIECE, /* piece information */
NULL,           /* callback context */
NULL,           /* callback function */
0,              /* character set ID - default */
SQLCS_IMPLICIT); /* character set form */

/* First piece for the first locator is read here.
* bufp[0]          => Buffer pointer into which data is read.
* char_amtp[0 ]    => Number of characters read in current buffer
*
*/

while ( st == OCI_NEED_DATA)
{
st =  OCILobArrayRead(<service context>, <error handle>,
&array_iter, /* array size */
lob_array, /* array of locators */
NULL,      /* array of byte amounts */
char_amtp, /* array of char amounts */
offset,    /* array of offsets */
(void **)bufp,      /* array of read buffers */
bufl,      /* array of buffer lengths */
OCI_NEXT_PIECE, /* piece information */
NULL,           /* callback context */
NULL,           /* callback function */
0,              /* character set ID - default */
SQLCS_IMPLICIT);

/* array_iter returns the index of the current array element for which
* data is read. for example, aray_iter = 1 implies first locator,
* array_iter = 2 implies second locator and so on.
*
* lob_array[ array_iter - 1]=> Lob locator for which data is read.
* bufp[array_iter - 1]      => Buffer pointer into which data is read.
* char_amtp[array_iter - 1]=>Number of characters read in current buffer
*/

...
/* Consume the data here */
...
}

Syntax

Use the following syntax references for the OCI programmatic environment:

C (OCI): Oracle Call Interface Programmer's Guide "LOB Functions" — OCILobArrayRead().

Example

An example is provided in the following programmatic environment:

OCI: lreadarr.c

Reading a Portion of a LOB (SUBSTR)

This section describes how to read a portion of a LOB using SUBSTR.

Syntax

Use the following syntax references for each programmatic environment:

- PL/SQL (DBM_LOB Package): Oracle Database PL/SQL Packages and Types Reference "DBMS_LOB" — SUBSTR, OPEN, CLOSE

- C (OCI): There is no applicable syntax reference for this use case.

- C++ (OCCI): Oracle C++ Call Interface Programmer's Guide

- COBOL (Pro*COBOL) Pro*COBOL Programmer's Guide for information on LOBs, usage notes on LOB Statements, and embedded SQL and precompiler directives — ALLOCATE, LOB OPEN, LOB READ, LOB CLOSE.

- C/C++ (Pro*C/C++): Pro*C/C++ Programmer's Guide Appendix F, "Embedded SQL Statements and Directives" — LOB READ. See PL/SQL DBMS_LOB.SUBSTR.

- Visual Basic (OO4O) (Oracle Objects for OLE (OO4O) Online Help): From Help Topics, Contents tab, select OO4O Automation Server > OBJECTS > Orablob > PROPERTIES > offset, chunksize, and >OBJECTS > Oraclob > METHODS > read

- Java (JDBC): Oracle Database JDBC Developer's Guide and Reference, "Working With LOBs" — Creating and Populating a BLOB or CLOB Column.

Examples

Examples are provided in the following programmatic environments:

- PL/SQL (DBMS_LOB Package): lsubstr.sql

- OCI: No example is provided with this release.

- C++ (OCCI): No example is provided with this release.

- Visual Basic (OO4O): lsubstr.bas

- Java (JDBC): lsubstr.java

Comparing All or Part of Two LOBs

This section describes how to compare all or part of two LOBs.

Syntax

Use the following syntax references for each programmatic environment:

- PL/SQL (DBM_LOB Package): Oracle Database PL/SQL Packages and Types Reference "DBMS_LOB" — COMPARE.

- C (OCI): There is no applicable syntax reference for this use case.

- C++ (OCCI): Oracle C++ Call Interface Programmer's Guide

- COBOL (Pro*COBOL) Pro*COBOL Programmer's Guide or information on LOBs, usage notes on LOB Statements, and embedded SQL and precompiler directives — EXECUTE. Also reference PL/SQL DBMS_LOB.COMPARE.

- C/C++ (Pro*C/C++): Pro*C/C++ Programmer's Guide Appendix F, "Embedded SQL Statements and Directives" — EXECUTE. Also reference PL/SQL DBMS_LOB.COMPARE.

- Visual Basic (OO4O) (Oracle Objects for OLE (OO4O) Online Help): From Help Topics, Contents tab, select OO4O Automation Server > OBJECTS > Oradynaset > METHODS > movenext

- Java (JDBC): Oracle Database JDBC Developer's Guide and Reference, "Working With LOBs" — Creating and Populating a BLOB or CLOB Column.

Examples

Examples are provided in the following programmatic environments:

- PL/SQL (DBMS_LOB Package): lcompare.sql

- C (OCI): No example is provided with this release.

- C++ (OCCI): No example is provided with this release.

- Visual Basic (OO4O): lcompare.bas

- Java (JDBC): lcompare.java

Patterns: Checking for Patterns in a LOB Using INSTR

This section describes how to see if a pattern exists in a LOB using INSTR.

Syntax

Use the following syntax references for each programmatic environment:

- PL/SQL (DBM_LOB Package): Oracle Database PL/SQL Packages and Types Reference "DBMS_LOB" — INSTR.

- C (OCI): There is no applicable syntax reference for this use case.

- C++ (OCCI): Oracle C++ Call Interface Programmer's Guide

- COBOL (Pro*COBOL) Pro*COBOL Programmer's Guide for information on LOBs, usage notes on LOB statements, and embedded SQL and precompiler directives — EXECUTE. Also reference PL/SQL DBMS_LOB.INSTR.

- C/C++ (Pro*C/C++): Pro*C/C++ Programmer's Guide Appendix F, "Embedded SQL Statements and Directives" — EXECUTE. Also reference PL/SQL DBMS_LOB.INSTR.

- Visual Basic (OO4O): There is no applicable syntax reference for this use case.

- Java (JDBC): Oracle Database JDBC Developer's Guide and Reference Chapter 7, "Working With LOBs" — Creating and Populating a BLOB or CLOB Column.

Examples

Examples are provided in the following programmatic environments:

- PL/SQL (DBMS_LOB Package): linstr.sql

- C (OCI): No example is provided with this release.

- C++ (OCCI): No example is provided with this release.

- Visual Basic (OO4O): No example is provided with this release.

- Java (JDBC): linstr.java

Length: Determining the Length of a LOB

This section describes how to determine the length of a LOB.

Syntax

Use the following syntax references for each programmatic environment:

- PL/SQL (DBM_LOB Package): Oracle Database PL/SQL Packages and Types Reference "DBMS_LOB" — GETLENGTH

- C (OCI): Oracle Call Interface Programmer's Guide "LOB Functions" — OCILobGetLength2().

- C++ (OCCI): Oracle C++ Call Interface Programmer's Guide

- COBOL (Pro*COBOL) Pro*COBOL Programmer's Guide for information on LOBs, usage notes on LOB Statements, and embedded SQL and precompiler directives — LOB DESCRIBE.

- C/C++ (Pro*C/C++): Pro*C/C++ Programmer's Guide Appendix F, "Embedded SQL Statements and Directives" — LOB DESCRIBE ...GET LENGTH...

- Visual Basic (OO4O) (Oracle Objects for OLE (OO4O) Online Help): From Help Topics, Contents tab, select OO4O Automation Server > OBJECTS > Oradynaset > PROPERTIES > fields

- Java (JDBC): Oracle Database JDBC Developer's Guide and Reference, "Working With LOBs" — Creating and Populating a BLOB or CLOB Column.

Examples

Examples are provided in the following programmatic environments:

- PL/SQL (DBMS_LOB Package) llength.sql

- OCI: llength.c

- C++ (OCCI): No example is provided with this release.

- Visual Basic (OO4O): llength.bas

- Java (JDBC): llength.java

Copying All or Part of One LOB to Another LOB

This section describes how to copy all or part of a LOB to another LOB. These APIs copy an amount of data you specify from a source LOB to a destination LOB.

Usage Notes

Note the following issues when using this API.

Specifying Amount of Data to Copy

The value you pass for the amount parameter to the DBMS_LOB.COPY function must be one of the following:

- An amount less than or equal to the actual size of the data you are loading.

- The maximum allowable LOB size: DBMS_LOB.LOBMAXSIZE.Passing this value causes the function to read the entire LOB. This is a useful technique for reading the entire LOB without introspecting the size of the LOB.

Note that for character data, the amount is specified in characters, while for binary data, the amount is specified in bytes.

Locking the Row Prior to Updating

If you plan to update a LOB value, then you must lock the row containing the LOB prior to updating. While the SQL INSERT and UPDATE statements implicitly lock the row, locking is done explicitly by means of a SQL SELECT FOR UPDATE statement in SQL and PL/SQL programs, or by using an OCI pin or lock function in OCI programs.

For more details on the state of the locator after an update, refer to "Example of Updating LOBs Through Updated Locators".

Syntax

See the following syntax references for each programmatic environment:

- PL/SQL (DBM_LOB Package): Oracle Database PL/SQL Packages and Types Reference "DBMS_LOB" — COPY

- C (OCI): Oracle Call Interface Programmer's Guide "LOB Functions" — OCILobCopy2

- C++ (OCCI): Oracle C++ Call Interface Programmer's Guide

- COBOL (Pro*COBOL) Pro*COBOL Programmer's Guide for information on LOBs, usage notes on LOB Statements, and embedded SQL and precompiler directives — LOB COPY. Also reference PL/SQL DBMS_LOB.COPY.

- C/C++ (Pro*C/C++): Pro*C/C++ Programmer's Guide for information on embedded SQL statements and directives — LOB COPY

- Visual Basic (OO4O) (Oracle Objects for OLE (OO4O) Online Help): From Help Topics, Contents tab, select OO4O Automation Server > OBJECTS > Orablob > METHODS > copy, and > OBJECTS > Oradynaset > METHODS > movenext, edit

- Java (JDBC): Oracle Database JDBC Developer's Guide and Reference, "Working With LOBs" — Creating and Populating a BLOB or CLOB Column.

Examples

Examples are provided in the following programmatic environments:

- PL/SQL (DBMS_LOB Package): lcopy.sql

- OCI: lcopy.c

- Visual Basic (OO4O): lcopy.bas

- Java (JDBC): lcopy.java

Copying a LOB Locator

This section describes how to copy a LOB locator. Note that different locators may point to the same or different data, or to current or outdated data.

Note:

Assigning one LOB to another using PL/SQL entails using the ":=" sign. This is an advanced topic that is discussed in more detail in "Read Consistent Locators".

Syntax

Use the following syntax references for each programmatic environment:

- PL/SQL (DBM_LOB Package): Refer to "Read Consistent Locators" for information on assigning one lob locator to another.

- C (OCI): Oracle Call Interface Programmer's Guide "LOB Functions" — OCILobAssign(), OCILobIsEqual().

- C++ (OCCI): Oracle C++ Call Interface Programmer's Guide

- COBOL (Pro*COBOL) Pro*COBOL Programmer's Guide for information on LOBs, usage notes on LOB Statements, and embedded SQL and precompiler directives — ALLOCATE, LOB ASSIGN.

- C/C++ (Pro*C/C++): Pro*C/C++ Programmer's Guide Appendix F, "Embedded SQL Statements and Directives" — SELECT, LOB ASSIGN

- Visual Basic (OO4O) (Oracle Objects for OLE (OO4O) Online Help): From Help Topics, Contents tab, select OO4O Automation Server > OBJECTS > Orablob > METHODS > copy

- Java (JDBC): Oracle Database JDBC Developer's Guide and Reference Chapter 7, "Working With LOBs" — Creating and Populating a BLOB or CLOB Column.

Examples

Examples are provided in the following programmatic environments:

- PL/SQL (DBMS_LOB Package): lcopyloc.sql

- OCI: lcopyloc.c

- C++ (OCCI): No example is provided with this release.

- Visual Basic (OO4O): lcopyloc.bas

- Java (JDBC): lcopyloc.java

Equality: Checking If One LOB Locator Is Equal to Another

This section describes how to determine whether one LOB locator is equal to another. If two locators are equal, then this means that they refer to the same version of the LOB data.

See Also:

- Table 14-1, "Environments Supported for Basic LOB APIs"

- "Read Consistent Locators"

Syntax

Use the following syntax references for each programmatic environment:

- C (OCI): Oracle Call Interface Programmer's Guide "LOB Functions" — OCILobAssign(), OCILobIsEqual().

- C++ (OCCI): Oracle C++ Call Interface Programmer's Guide

- COBOL (Pro*COBOL): There is no applicable syntax reference for this use case.

- C/C++ (Pro*C/C++): Pro*C/C++ Programmer's Guide Appendix F, "Embedded SQL Statements and Directives" — LOB ASSIGN

- Visual Basic (OO4O): There is no applicable syntax reference for this use case.

- Java (JDBC): Oracle Database JDBC Developer's Guide and Reference, "Working With LOBs" — Creating and Populating a BLOB or CLOB Column.

Examples

Examples are provided in the following programmatic environments:

- PL/SQL: No example is provided with this release.

- OCI: lequal.c

- C++ (OCCI): No example is provided with this release.

- Visual Basic (OO4O): No example is provided with this release.

- Java (JDBC): lequal.java

Determining Whether LOB Locator Is Initialized

This section describes how to determine whether a LOB locator is initialized.

See Also:

Table 14-1, "Environments Supported for Basic LOB APIs"

Syntax

Use the following syntax references for each programmatic environment:

- PL/SQL (DBMS_LOB Package): There is no applicable syntax reference for this use case.

- C (OCI): Oracle Call Interface Programmer's Guide "LOB Functions" — OCILobLocatorIsInit().

- C++ (OCCI): Oracle C++ Call Interface Programmer's Guide

- COBOL (Pro*COBOL): There is no applicable syntax reference for this use case.

- C/C++ (Pro*C/C++) Pro*C/C++ Programmer's Guide Appendix F, "Embedded SQL Statements and Directives". See C(OCI), OCILobLocatorIsInit().

- Visual Basic (OO4O): There is no applicable syntax reference for this use case.

- Java (JDBC): There is no applicable syntax reference for this use case.

Examples

Examples are provided in the following programmatic environments:

- PL/SQL (DBMS_LOB Package): No example is provided with this release.

- OCI: linit.c

- C (OCCI)): No example is provided with this release.

- Visual Basic (OO4O): No example is provided with this release.

- Java (JDBC): No example is provided with this release.

Appending to a LOB

This section describes how to write-append the contents of a buffer to a LOB.

See Also:

Table 14-1, "Environments Supported for Basic LOB APIs"

Usage Notes

Note the following issues regarding usage of this API.

Writing Singly or Piecewise

The writeappend operation writes a buffer to the end of a LOB.

For OCI, the buffer can be written to the LOB in a single piece with this call; alternatively, it can be rendered piecewise using callbacks or a standard polling method.

Writing Piecewise: When to Use Callbacks or Polling

If the value of the piece parameter is OCI_FIRST_PIECE, then data must be provided through callbacks or polling.

- If a callback function is defined in the cbfp parameter, then this callback function will be called to get the next piece after a piece is written to the pipe. Each piece will be written from bufp.

- If no callback function is defined, then OCILobWriteAppend2() returns the OCI_NEED_DATA error code. The application must call OCILobWriteAppend2() again to write more pieces of the LOB. In this mode, the buffer pointer and the length can be different in each call if the pieces are of different sizes and from different locations. A piece value of OCI_LAST_PIECE terminates the piecewise write.

Locking the Row Prior to Updating Prior to updating a LOB value using the PL/SQL DBMS_LOB package or the OCI, you must lock the row containing the LOB. While the SQL INSERT and UPDATE statements implicitly lock the row, locking is done explicitly by means of an SQL SELECT FOR UPDATE statement in SQL and PL/SQL programs, or by using an OCI pin or lock function in OCI programs.

For more details on the state of the locator after an update, refer to "Example of Updating LOBs Through Updated Locators".

Syntax

Use the following syntax references for each programmatic environment:

- PL/SQL (DBM_LOB Package): Oracle Database PL/SQL Packages and Types Reference "DBMS_LOB" — WRITEAPPEND

- C (OCI): Oracle Call Interface Programmer's Guide "LOB Functions" — OCILobWriteAppend2()

- C++ (OCCI): Oracle C++ Call Interface Programmer's Guide

- COBOL (Pro*COBOL) Pro*COBOL Programmer's Guide for information on LOBs, usage notes on LOB statements, and embedded SQL and precompiler directives — LOB WRITE APPEND.

- C/C++ (Pro*C/C++): Pro*C/C++ Programmer's Guide Appendix F, "Embedded SQL Statements and Directives" — LOB WRITE APPEND

- Visual Basic (OO4O): No syntax reference is provided with this release.

- Java (JDBC): Oracle Database JDBC Developer's Guide and Reference Chapter 7, "Working With LOBs" — Creating and Populating a BLOB or CLOB Column.

Examples

Examples are provided in the following programmatic environments:

- PL/SQL (DBMS_LOB Package): lwriteap.sql

- OCI: lwriteap.c

- C++ (OCCI): No example is provided with this release.

- Visual Basic (OO4O): No example is provided with this release.

- Java (JDBC): lwriteap.java

Writing Data to a LOB

This section describes how to write the contents of a buffer to a LOB.

See Also:

- Table 14-1, "Environments Supported for Basic LOB APIs"

- Reading Data from a LOB

Usage Notes

Note the following issues regarding usage of this API.

Stream Write

The most efficient way to write large amounts of LOB data is to use OCILobWrite2() with the streaming mechanism enabled, and using polling or a callback. If you know how much data will be written to the LOB, then specify that amount when calling OCILobWrite2(). This ensures that LOB data on the disk is contiguous. Apart from being spatially efficient, the contiguous structure of the LOB data will make for faster reads and writes in subsequent operations.

Chunk Size

A chunk is one or more Oracle blocks. You can specify the chunk size for the LOB when creating the table that contains the LOB. This corresponds to the data size used by Oracle Database when accessing or modifying the LOB value. Part of the chunk is used to store system-related information and the rest stores the LOB value. The API you are using has a function that returns the amount of space used in the LOB chunk to store the LOB value. In PL/SQL use DBMS_LOB.GETCHUNKSIZE. In OCI, use OCILobGetChunkSize().

Use a Multiple of the Returned Value to Improve Write Performance

You will improve performance if you run write requests using a multiple of the value returned by one of these functions. The reason for this is that the LOB chunk is versioned for every write operation. If all writes are done on a chunk basis, then no extra or excess versioning is incurred or duplicated. If it is appropriate for your application, then you should batch writes until you have enough for an entire chunk instead of issuing several LOB write calls that operate on the same LOB chunk.

Locking the Row Prior to Updating

Prior to updating a LOB value using the PL/SQL DBMS_LOB Package or OCI, you must lock the row containing the LOB. While the SQL INSERT and UPDATE statements implicitly lock the row, locking is done explicitly by means of a SQL SELECT FOR UPDATE statement in SQL and PL/SQL programs, or by using an OCI pin or lock function in OCI programs.

For more details on the state of the locator after an update, refer to "Example of Updating LOBs Through Updated Locators".

Using DBMS_LOB.WRITE to Write Data to a BLOB

When you are passing a hexadecimal string to DBMS_LOB.WRITE() to write data to a BLOB, use the following guidelines:

- The amount parameter should be <= the buffer length parameter

- The length of the buffer should be ((amount*2) - 1). This guideline exists because the two characters of the string are seen as one hexadecimal character (and an implicit hexadecimal-to-raw conversion takes place), that is, every two bytes of the string are converted to one raw byte.

The following example is correct:

declare
blob_loc  BLOB;
rawbuf RAW(10);
an_offset INTEGER := 1;
an_amount BINARY_INTEGER := 10;
BEGIN
select blob_col into blob_loc from a_table
where id = 1;
rawbuf := '1234567890123456789';
dbms_lob.write(blob_loc, an_amount, an_offset,
rawbuf);
commit;
END;

Replacing the value for an_amount in the previous example with the following values, yields error message, ora_21560:

an_amount BINARY_INTEGER := 11;

or

an_amount BINARY_INTEGER := 19;

Syntax

Use the following syntax references for each programmatic environment:

- PL/SQL (DBM_LOB Package): Oracle Database PL/SQL Packages and Types Reference "DBMS_LOB" — WRITE

- C (OCI): Oracle Call Interface Programmer's Guide "LOB Functions" — OCILobWrite2().

- C++ (OCCI): Oracle C++ Call Interface Programmer's Guide

- COBOL (Pro*COBOL) Pro*COBOL Programmer's Guide for information on LOBs, usage notes on LOB statements, and embedded SQL and precompiler directives — LOB WRITE.

- C/C++ (Pro*C/C++): Pro*C/C++ Programmer's Guide Appendix F, "Embedded SQL Statements and Directives" — LOB WRITE

- Visual Basic (OO4O): (Oracle Objects for OLE (OO4O) Online Help): From Help Topics, Contents tab, select OO4O Automation Server > OBJECTS > Orablob > METHODS > write, copyfromfile

- Java (JDBC): Oracle Database JDBC Developer's Guide and Reference Chapter 7, "Working With LOBs" — Creating and Populating a BLOB or CLOB Column.

Examples

Examples are provided in the following programmatic environments:

- PL/SQL (DBMS_LOB Package): lwrite.sql

- OCI: lwrite.c

- Visual Basic (OO4O): lwrite.bas

- Java (JDBC): lwrite.java

LOB Array Write

This section describes how to write LOB data for multiple locators in one round trip, using OCILobArrayWrite().

Usage Notes

See Also:

"LOB Array Read" for examples of Array read/write.

LOB Array Write in Polling Mode

The following example writes 10Kbytes of data for each of 10 locators with a 1K buffer size. OCILobArrayWrite() has to be called 100 (10*10 ) times to write all the data. The function is used in a similar manner to OCILobWrite2().

/* Fetch the locators */
...

/* array_iter parameter indicates the number of locators in the array read.
* It is an IN parameter for the 1st call in polling and is ignored as IN
* parameter for subsequent calls. As an OUT parameter it indicates the locator
* index for which the piece is written.
*/

ub4    array_iter = 10;
char  *bufp[10];
oraub8 bufl[10];
oraub8 char_amtp[10];
oraub8 offset[10];
sword  st;
int    i, j;

for (i=0; i<10; i++)
{
bufp[i] = (char *)malloc(1000);
bufl[i] = 1000;
/* Fill bufp here. */
...
offset[i] = 1;
char_amtp[i] = 10000;       /* Single byte fixed width char set. */
}

for (i  = 1; i <= 10; i++)
{
/* Fill up bufp[i-1] here.  The first piece for ith locator would be written from
bufp[i-1] */
...
st =  OCILobArrayWrite(<service context>, <error handle>,
&array_iter, /* array size */
lob_array,   /* array of locators */
NULL,        /* array of byte amounts */
char_amtp,   /* array of char amounts */
offset,      /* array of offsets */
(void **)bufp,        /* array of write buffers */
bufl,        /* array of buffer lengths */
OCI_FIRST_PIECE, /* piece information */
NULL,            /* callback context */
NULL,            /* callback function */
0,               /* character set ID - default */
SQLCS_IMPLICIT); /* character set form */

for ( j = 2; j < 10; j++)
{
/* Fill up bufp[i-1] here.  The jth piece for ith locator would be written from
bufp[i-1] */
...
st =  OCILobArrayWrite(<service context>, <error handle>,
&array_iter, /* array size */
lob_array,   /* array of locators */
NULL,        /* array of byte amounts */
char_amtp,   /* array of char amounts */
offset,      /* array of offsets */
(void **)bufp,        /* array of write buffers */
bufl,        /* array of buffer lengths */
OCI_NEXT_PIECE, /* piece information */
NULL,           /* callback context */
NULL,           /* callback function */
0,              /* character set ID - default */
SQLCS_IMPLICIT);

/* array_iter returns the index of the current array element for which
* data is being written. for example, aray_iter = 1 implies first locator,
* array_iter = 2 implies second locator and so on. Here i = array_iter.
*
* lob_array[ array_iter - 1] => Lob locator for which data is written.
* bufp[array_iter - 1]       => Buffer pointer from which data is written.
* char_amtp[ array_iter - 1] => Number of characters written in
* the piece just written
*/
}

/* Fill up bufp[i-1] here.  The last piece for ith locator would be written from
bufp[i -1] */
...
st =  OCILobArrayWrite(<service context>, <error handle>,
&array_iter, /* array size */
lob_array,   /* array of locators */
NULL,        /* array of byte amounts */
char_amtp,   /* array of char amounts */
offset,      /* array of offsets */
(void **)bufp,        /* array of write buffers */
bufl,        /* array of buffer lengths */
OCI_LAST_PIECE,  /* piece information */
NULL,            /* callback context */
NULL,            /* callback function */
0,               /* character set ID - default */
SQLCS_IMPLICIT);
}

...

LOB Array Write with Callback

The following example writes 10Kbytes of data for each of 10 locators with a 1K buffer size. A total of 100 pieces need to be written (10 pieces for each locator). The first piece is provided by the OCILobArrayWrite() call. The callback function is called 99 times to get the data for subsequent pieces to be written.

/* Fetch the locators */
...

ub4    array_iter = 10;
char  *bufp[10];
oraub8 bufl[10];
oraub8 char_amtp[10];
oraub8 offset[10];
sword  st;

for (i=0; i<10; i++)
{
bufp[i] = (char *)malloc(1000);
bufl[i] = 1000;
offset[i] = 1;
char_amtp[i] = 10000;       /* Single byte fixed width char set. */
}

st =  OCILobArrayWrite(<service context>, <error handle>,
&array_iter, /* array size */
lob_array,   /* array of locators */
NULL,        /* array of byte amounts */
char_amtp,   /* array of char amounts */
offset,      /* array of offsets */
(void **)bufp,        /* array of write buffers */
bufl,        /* array of buffer lengths */
OCI_FIRST_PIECE,  /* piece information */
ctx,              /* callback context */
cbk_write_lob     /* callback function */
0,                /* character set ID - default */
SQLCS_IMPLICIT);

...

/* Callback function for LOB array write. */
sb4 cbk_write_lob(dvoid *ctxp, ub4 array_iter, dvoid *bufxp, oraub8 *lenp,
ub1 *piecep, ub1 *changed_bufpp, oraub8 *changed_lenp)
{
static ub4 piece_count = 0;
piece_count++;

printf (" %dth piece written  for %dth locator \n\n", piece_count, array_iter);

/*-- code to fill bufxp with data goes here. *lenp should reflect the  size and
*   should be less than or equal to MAXBUFLEN -- */
/* --Optional code to set changed_bufpp and changed_lenp if the buffer needs to
*   be changed dynamically --*/

if (this is the last data buffer for current locator)
*piecep = OCI_LAST_PIECE;
else if (this is the first data buffer for the next locator)
*piecep = OCI_FIRST_PIECE;
piece_count = 0;
else
*piecep = OCI_NEXT_PIECE;

return OCI_CONTINUE;
}
...

Polling LOB Data in Array Write

The next example is polling LOB data in OCILobArrayWrite() with variable amtp, bufl, and offset.

/* Fetch the locators */
...

ub4    array_iter = 10;
char  *bufp[10];
oraub8 bufl[10];
oraub8 char_amtp[10];
oraub8 offset[10];
sword  st;
int    i, j;
int piece_count;

for (i=0; i<10; i++)
{
bufp[i] = (char *)malloc(1000);
bufl[i] = 1000;
/* Fill bufp here. */
...
offset[i] = 1;
char_amtp[i] = 10000;       /* Single byte fixed width char set. */
}

/* For 3rd locator write data in 500 bytes piece from offset 101. Amount
* is 2000, that is, total number of pieces will be 2000/500 = 4.
*/
offset[2] = 101; bufl[2] = 500; char_amtp[2] = 2000;

/* For 6th locator write data in 100 bytes piece from offset 51. Amount
* is 0 indicating pure polling, that is, data will be written
* till OCI_LAST_PIECE
*/
offset[5] = 51;  bufl[5] = 100; char_amtp[5] = 0;

/* For 8th locator write 100 bytes of data in one piece. Note amount
* is less than buffer length indicating single piece write.
*/
offset[7] = 61;  bufl[7] = 200; char_amtp[7] = 100;

for (i  = 1; i <= 10; i++)
{
/* Fill up bufp[i-1] here.  The first piece for ith locator would be written from
bufp[i-1] */
...
/* Calculate number of pieces need to be written */
piece_count = char_amtp[i-1]/bufl[i-1];

/* Single piece case */
if (char_amtp[i-1] <= bufl[i-1])
piece_count = 1;

/* Zero amount indicates pure polling. So we can write as many
* pieces as needed. Let us write 50 pieces.
*/
if (char_amtp[i-1] == 0)
piece_count = 50;

st =  OCILobArrayWrite(<service context>, <error handle>,
&array_iter, /* array size */
lob_array,   /* array of locators */
NULL,        /* array of byte amounts */
char_amtp,   /* array of char amounts */
offset,      /* array of offsets */
(void **)bufp,        /* array of write buffers */
bufl,        /* array of buffer lengths */
OCI_FIRST_PIECE, /* piece information */
NULL,            /* callback context */
NULL,            /* callback function */
0,               /* character set ID - default */
SQLCS_IMPLICIT); /* character set form */

for ( j = 2; j < piece_count; j++)
{
/* Fill up bufp[i-1] here. The jth piece for ith locator would be written
* from bufp[i-1] */
...
st =  OCILobArrayWrite(<service context>, <error handle>,
&array_iter, /* array size */
lob_array,   /* array of locators */
NULL,        /* array of byte amounts */
char_amtp,   /* array of char amounts */
offset,      /* array of offsets */
(void **)bufp,        /* array of write buffers */
bufl,        /* array of buffer lengths */
OCI_NEXT_PIECE, /* piece information */
NULL,           /* callback context */
NULL,           /* callback function */
0,              /* character set ID - default */
SQLCS_IMPLICIT);

/* array_iter returns the index of the current array element for which
* data is being written. for example, aray_iter = 1 implies first locator,
* array_iter = 2 implies second locator and so on. Here i = array_iter.
*
* lob_array[ array_iter - 1] => Lob locator for which data is written.
* bufp[array_iter - 1]       => Buffer pointer from which data is written.
* char_amtp[ array_iter - 1] => Number of characters written in
* the piece just written
*/
}

/* Fill up bufp[i-1] here.  The last piece for ith locator would be written from
* bufp[i -1] */
...

/* If piece_count is 1 it is a single piece write. */
if (piece_count[i] != 1)
st =  OCILobArrayWrite(<service context>, <error handle>,
&array_iter, /* array size */
lob_array,   /* array of locators */
NULL,        /* array of byte amounts */
char_amtp,   /* array of char amounts */
offset,      /* array of offsets */
(void **)bufp,        /* array of write buffers */
bufl,        /* array of buffer lengths */
OCI_LAST_PIECE,  /* piece information */
NULL,            /* callback context */
NULL,            /* callback function */
0,               /* character set ID - default */
SQLCS_IMPLICIT);
}

...

Syntax

Use the following syntax references for the OCI programmatic environment:

C (OCI): Oracle Call Interface Programmer's Guide "LOB Functions" — OCILobArrayWrite().

Example

An example is provided in the following programmatic environment:

OCI: lwritearr.c

Trimming LOB Data

This section describes how to trim a LOB to the size you specify.

See Also:

Table 14-1, "Environments Supported for Basic LOB APIs"

Usage Notes

Note the following issues regarding usage of this API.

Locking the Row Prior to Updating

Prior to updating a LOB value using the PL/SQL DBMS_LOB Package, or OCI, you must lock the row containing the LOB. While the SQL INSERT and UPDATE statements implicitly lock the row, locking is done explicitly by means of:

- A SELECT FOR UPDATE statement in SQL and PL/SQL programs.

- An OCI pin or lock function in OCI programs.

For more details on the state of the locator after an update, refer to "Example of Updating LOBs Through Updated Locators".

Syntax

Use the following syntax references for each programmatic environment:

- PL/SQL (DBM_LOB Package): Oracle Database PL/SQL Packages and Types Reference "DBMS_LOB" — TRIM

- C (OCI): Oracle Call Interface Programmer's Guide "LOB Functions" — OCILobTrim2().

- C++ (OCCI): Oracle C++ Call Interface Programmer's Guide

- COBOL (Pro*COBOL) Pro*COBOL Programmer's Guide for information on LOBs, usage notes on LOB statements, and embedded SQL and precompiler directives — LOB TRIM.

- C/C++ (Pro*C/C++): Pro*C/C++ Programmer's Guide Appendix F, "Embedded SQL and Precompiler Directives" — LOB TRIM

- Visual Basic (OO4O) (Oracle Objects for OLE (OO4O) Online Help): From Help Topics, Contents tab, select OO4O Automation Server > OBJECTS > Orablob > METHODS > trim

- Java (JDBC): Oracle Database JDBC Developer's Guide and Reference Chapter 7, "Working With LOBs" — Creating and Populating a BLOB or CLOB Column.

Examples

Examples are provided in the following programmatic environments:

- PL/SQL (DBMS_LOB Package): ltrim.sql

- OCI: ltrim.c

- C++ (OCCI): No example is provided with this release.

- Visual Basic (OO4O): ltrim.bas

- Java (JDBC): ltrim.java

Erasing Part of a LOB

This section describes how to erase part of a LOB.

See Also:

Table 14-1, "Environments Supported for Basic LOB APIs"

Usage Notes

Note the following issues regarding usage of this API.

Locking the Row Prior to Updating

Prior to updating a LOB value using the PL/SQL DBMS_LOB Package or OCI, you must lock the row containing the LOB. While INSERT and UPDATE statements implicitly lock the row, locking is done explicitly by means of a SELECT FOR UPDATE statement in SQL and PL/SQL programs, or by using the OCI pin or lock function in OCI programs.

For more details on the state of the locator after an update, refer to"Example of Updating LOBs Through Updated Locators".

Syntax

Use the following syntax references for each programmatic environment:

- PL/SQL (DBM_LOB Package): Oracle Database PL/SQL Packages and Types Reference "DBMS_LOB" — ERASE

- C (OCI): Oracle Call Interface Programmer's Guide "LOB Functions" — OCILobErase2().

- C++ (OCCI): Oracle C++ Call Interface Programmer's Guide

- COBOL (Pro*COBOL) Pro*COBOL Programmer's Guide for information on LOBs, usage notes on LOB statements, and embedded SQL and precompiler directives — LOB ERASE.

- C/C++ (Pro*C/C++): Pro*C/C++ Programmer's Guide Appendix F, "Embedded SQL and Precompiler Directives" — LOB ERASE

- Visual Basic (OO4O) (Oracle Objects for OLE (OO4O) Online Help): From Help Topics, Contents tab, select OO4O Automation Server > OBJECTS > Orablob > METHODS > erase

- Java (JDBC): Oracle Database JDBC Developer's Guide and Reference, "Working With LOBs" — Creating and Populating a BLOB or CLOB Column.

Examples

Examples are provided in the following programmatic environments:

- PL/SQL (DBMS_LOB Package): lerase.sql

- OCI: lerase.c

- C++ (OCCI): No example is provided with this release.

- Visual Basic (OO4O): lerase.bas

- Java (JDBC): lerase.java

Enabling LOB Buffering

This section describes how to enable LOB buffering.

See Also:

Table 14-1, "Environments Supported for Basic LOB APIs"

Usage Notes

Enable LOB buffering when you are performing a small read or write of data. Once you have completed these tasks, you must disable buffering before you can continue with any other LOB operations.

Note:

- You must flush the buffer in order to make your modifications persistent.

- Do not enable buffering for the stream read and write involved in checkin and checkout.

For more information, refer to "LOB Buffering Subsystem".

Syntax

Use the following syntax references for each programmatic environment:

- PL/SQL: This API is not available in any supplied PL/SQL packages.

- C (OCI): Oracle Call Interface Programmer's Guide "LOB Functions" — OCIEnableLobBuffering(), OCIDisableLobBuffering(), OCIFlushBuffer().

- C++ (OCCI): Oracle C++ Call Interface Programmer's Guide

- COBOL (Pro*COBOL) Pro*COBOL Programmer's Guide for information on LOBs, usage notes on LOB statements, and embedded SQL and precompiler directives — LOB ENABLE BUFFERING.

- C/C++ (Pro*C/C++): Pro*C/C++ Programmer's Guide Appendix F, "Embedded SQL and Precompiler Directives" — LOB ENABLE BUFFERING

- Visual Basic (OO4O) (Oracle Objects for OLE (OO4O) Online Help): From Help Topics, Contents tab, select OO4O Automation Server > OBJECTS > Orablob > METHODS > EnableBuffering

- Java (JDBC): There is no applicable syntax reference for this use case.

Examples

Examples are provided in the following programmatic environments:

- PL/SQL: No example is provided.

- C (OCI): No example is provided with this release. Using this API is similar to that described in the example, "Disabling LOB Buffering".

- C++ (OCCI): No example is provided with this release.

- Visual Basic (OO4O): lenbuf.bas

- Java (JDBC): No example provided.

Flushing the Buffer

This section describes how to flush the LOB buffer.

See Also:

Table 14-1, "Environments Supported for Basic LOB APIs"

Usage Notes

Enable buffering when performing a small read or write of data. Once you have completed these tasks, you must disable buffering before you can continue with any other LOB operations.

Notes:

- You must flush the buffer in order to make your modifications persistent.

- Do not enable buffering for the stream read and write involved in checkin and checkout.

For more information, refer to "LOB Buffering Subsystem".

Syntax

Use the following syntax references for each programmatic environment:

- PL/SQL (DBMS_LOB Package): There is no applicable syntax reference for this use case.

- C (OCI): Oracle Call Interface Programmer's Guide "LOB Functions" — OCIEnableLobBuffering(), OCIDisableLobBuffering(), OCIFlushBuffer().

- C++ (OCCI): Oracle C++ Call Interface Programmer's Guide

- COBOL (Pro*COBOL) Pro*COBOL Programmer's Guide for information on LOBs, usage notes on LOB statements, and embedded SQL and precompiler directives — LOB FLUSH BUFFER.

- C/C++ (Pro*C/C++): Pro*C/C++ Programmer's Guide Appendix F, "Embedded SQL Statements and Directives" — LOB FLUSH BUFFER.

- Visual Basic (OO4O) (Oracle Objects for OLE (OO4O) Online Help): From Help Topics, Contents tab, select OO4O Automation Server > OBJECTS > Orablob > METHODS > FlushBuffer.

- Java (JDBC): There is no applicable syntax reference for this use case.

Examples

Examples are provided in the following programmatic environments:

- PL/SQL (DBMS_LOB Package): No example is provided with this release.

- C (OCI): No example is provided with this release. Using this API is similar to that described in the example, "Disabling LOB Buffering".

- C++ (OCCI): No example is provided with this release.

- Visual Basic (OO4O): No example is provided with this release.

- Java (JDBC): No example is provided with this release.

Disabling LOB Buffering

This section describes how to disable LOB buffering.

See Also:

Table 14-1, "Environments Supported for Basic LOB APIs"

Usage Notes

Enable buffering when performing a small read or write of data. Once you have completed these tasks, you must disable buffering before you can continue with any other LOB operations.

Note:

- You must flush the buffer in order to make your modifications persistent.

- Do not enable buffering for the stream read and write involved in checkin and checkout.

For more information, refer to"LOB Buffering Subsystem"

Syntax

Use the following syntax references for each programmatic environment:

- PL/SQL (DBMS_LOB Package): There is no applicable syntax reference for this use case.

- C (OCI): Oracle Call Interface Programmer's Guide "LOB Functions" — OCIEnableLobBuffering(), OCIDisableLobBuffering(), OCIFlushBuffer().

- C++ (OCCI): Oracle C++ Call Interface Programmer's Guide

- COBOL (Pro*COBOL) Pro*COBOL Programmer's Guide for information on LOBs, usage notes on LOB statements, and embedded SQL and precompiler directives — LOB DISABLE BUFFER.

- C/C++ (Pro*C/C++): Pro*C/C++ Programmer's Guide Appendix F, "Embedded SQL Statements and Directives" — LOB DISABLE BUFFER

- Visual Basic (OO4O) (Oracle Objects for OLE (OO4O) Online Help): From Help Topics, Contents tab, select OO4O Automation Server > OBJECTS > Orablob > METHODS > DisableBuffering

- Java (JDBC): There is no applicable syntax reference for this use case.

Examples

Examples are provided in the following programmatic environments:

- PL/SQL (DBMS_LOB Package): No example is provided with this release.

- OCI: ldisbuf.c

- C++ (OCCI): No example is provided with this release.

- Visual Basic (OO4O): ldisbuf.bas

- Java (JDBC): No example is provided with this release.

Determining Whether a LOB instance Is Temporary

This section describes how to determine whether a LOB instance is temporary.

See Also:

Table 14-1, "Environments Supported for Basic LOB APIs"

Syntax

Use the following syntax references for each programmatic environment:

- PL/SQL (DBMS_LOB): Oracle Database PL/SQL Packages and Types Reference "DBMS_LOB" — ISTEMPORARY, FREETEMPORARY

- C (OCI): Oracle Call Interface Programmer's Guide "LOB Functions" — OCILobIsTemporary().

- COBOL (Pro*COBOL) Pro*COBOL Programmer's Guide for information on LOBs, usage notes on LOB statements, and embedded SQL and precompiler directives — LOB DESCRIBE, ISTEMPORARY.

- C/C++ (Pro*C/C++): Pro*C/C++ Programmer's Guide Appendix F, "Embedded SQL Statements and Directives" — LOB DESCRIBE...ISTEMPORARY

- Visual Basic (OO4O): There is no applicable syntax reference for this use case.

- Java (JDBC): Oracle Database JDBC Developer's Guide and Reference, "Working With LOBs" — Creating and Populating a BLOB or CLOB Column.

Examples

Examples are provided in the following programmatic environments:

- PL/SQL (DBMS_LOB Package): listemp.sql

- OCI: listemp.c

- Visual Basic (OO4O): No example is provided.

Java (JDBC): Determining Whether a BLOB Is Temporary

To see if a BLOB is temporary, the JDBC application can either use the isTemporary instance method to determine whether the current BLOB object is temporary, or pass the BLOB object to the static isTemporary method to determine whether the specified BLOB object is temporary. These two methods are defined inlistempb.java.

This JDBC API replaces previous workarounds that use DBMS_LOB.isTemporary().

To determine whether a CLOB is temporary, the JDBC application can either use the isTemporary instance method to determine whether the current CLOB object is temporary, or pass the CLOB object to the static isTemporary method. These two methods are defined in listempc.java.

Converting a BLOB to a CLOB

You can convert a BLOB instance to a CLOB using the PL/SQL procedure DBMS_LOB.CONVERTTOCLOB. This technique is convenient if you have character data stored in binary format that you want to store in a CLOB. You specify the character set of the binary data when calling this procedure. See Oracle Database PL/SQL Packages and Types Reference for details on syntax and usage of this procedure.

Converting a CLOB to a BLOB

You can convert a CLOB instance to a BLOB instance using the PL/SQL procedure DBMS_LOB.CONVERTTOBLOB. This technique is a convenient way to convert character data to binary data using LOB APIs. See Oracle Database PL/SQL Packages and Types Reference for details on syntax and usage of this procedure.

15 LOB APIs for BFILE Operations

This chapter describes APIs for operations that use BFILEs. APIs covered in this chapter are listed in Table 15-1.

The following information is given for each operation described in this chapter:

- Usage Notes provide implementation guidelines such as information specific to a given programmatic environment or datatype.

- Syntax refers you to the syntax reference documentation for each supported programmatic environment.

- Examples describe any setup tasks necessary to run the examples given. Demonstration files listed are available in subdirectories under $ORACLE_HOME/rdbms/demo/lobs/ named plsql, oci, vb, and java. The driver program lobdemo.sql is in /plsql and the driver program lobdemo.c is in /oci.

Note:

LOB APIs do not support loading data into BFILEs. See "Using SQL*Loader to Load LOBs" for details on techniques for loading data into BFILEs.

This chapter contains these topics:

- Supported Environments for BFILE APIs

- Accessing BFILEs

- Directory Objects

- BFILENAME and Initialization

- Characteristics of the BFILE Datatype

- BFILE Security

- Loading a LOB with BFILE Data

- Opening a BFILE with OPEN

- Opening a BFILE with FILEOPEN

- Determining Whether a BFILE Is Open Using ISOPEN

- Determining Whether a BFILE Is Open with FILEISOPEN

- Displaying BFILE Data

- Reading Data from a BFILE

- Reading a Portion of BFILE Data Using SUBSTR

- Comparing All or Parts of Two BFILES

- Checking If a Pattern Exists in a BFILE Using INSTR

- Determining Whether a BFILE Exists

- Getting the Length of a BFILE

- Assigning a BFILE Locator

- Getting Directory Object Name and File Name of a BFILE

- Updating a BFILE by Initializing a BFILE Locator

- Closing a BFILE with FILECLOSE

- Closing a BFILE with CLOSE

- Closing All Open BFILEs with FILECLOSEALL

- Inserting a Row Containing a BFILE

Supported Environments for BFILE APIs

Table 15-1, "Environments Supported for BFILE APIs" indicates which programmatic environments are supported for the APIs discussed in this chapter. The first column describes the operation that the API performs. The remaining columns indicate with "Yes" or "No" whether the API is supported in PL/SQL, OCI, COBOL, Pro*C/C++, Visual Basic (VB), and JDBC.

Table 15-1 Environments Supported for BFILE APIs

Operation

PL/SQL

OCI

COBOL

Pro*C/C++

VB

JDBC

Inserting a Row Containing a BFILE

Yes

Yes

Yes

Yes

Yes

Yes

Loading a LOB with BFILE Data

Yes

Yes

Yes

Yes

Yes

Yes

Opening a BFILE with FILEOPEN

Yes

Yes

No

No

No

Yes

Opening a BFILE with OPEN

Yes

Yes

Yes

Yes

Yes

Yes

Determining Whether a BFILE Is Open Using ISOPEN

Yes

Yes

Yes

Yes

Yes

Yes

Determining Whether a BFILE Is Open with FILEISOPEN

Yes

Yes

No

No

No

Yes

Displaying BFILE Data

Yes

Yes

Yes

Yes

Yes

Yes

Reading Data from a BFILE

Yes

Yes

Yes

Yes

Yes

Yes

Reading a Portion of BFILE Data Using SUBSTR

Yes

No

Yes

Yes

Yes

Yes

Comparing All or Parts of Two BFILES

Yes

No

Yes

Yes

Yes

Yes

Checking If a Pattern Exists in a BFILE Using INSTR

Yes

No

Yes

Yes

No

Yes

Determining Whether a BFILE Exists

Yes

Yes

Yes

Yes

Yes

Yes

Getting the Length of a BFILE

Yes

Yes

Yes

Yes

Yes

Yes

Assigning a BFILE Locator

Yes

Yes

Yes

Yes

No

Yes

Getting Directory Object Name and File Name of a BFILE

Yes

Yes

Yes

Yes

Yes

Yes

Updating a BFILE by Initializing a BFILE Locator

Yes

Yes

Yes

Yes

Yes

Yes

Closing a BFILE with FILECLOSE

Yes

Yes

No

No

Yes

Yes

Closing a BFILE with CLOSE

Yes

Yes

Yes

Yes

Yes

Yes

Closing All Open BFILEs with FILECLOSEALL

Yes

Yes

Yes

Yes

Yes

Yes

Accessing BFILEs

To access BFILEs use one of the following interfaces:

- OCI (Oracle Call Interface)

- PL/SQL (DBMS_LOB package)

- Precompilers, such as Pro*C/C++ and Pro*COBOL

- Oracle Objects for OLE (OO4O)

- Java (JDBC)

See Also:

Chapter 6, "Overview of Supplied LOB APIs" for information about supported environments for accessing BFILEs.

Directory Objects

The DIRECTORY object facilitates administering access and usage of BFILE datatypes. A DIRECTORY object specifies a logical alias name for a physical directory on the database server file system under which the file to be accessed is located. You can access a file in the server file system only if granted the required access privilege on DIRECTORY object. You can also use Enterprise Manager Web console to manage DIRECTORY objects.

See Also:

- CREATE DIRECTORY in Oracle Database SQL Reference

- support for directory objects in Oracle Enterprise Manager Extending Oracle Enterprise

Initializing a BFILE Locator

The DIRECTORY object also provides the flexibility to manage the locations of the files, instead of forcing you to hard-code the absolute path names of physical files in your applications. A directory object name is used in conjunction with the BFILENAME function, in SQL and PL/SQL, or the OCILobFileSetName() in OCI, for initializing a BFILE locator.

Note:

The database does not verify that the directory and path name you specify actually exist. You should take care to specify a valid directory in your operating system. If your operating system uses case-sensitive path names, then be sure you specify the directory in the correct format. There is no need to specify a terminating slash (for example, /tmp/ is not necessary, simply use /tmp).

Directory specifications cannot contain ".." anywhere in the path (for example, /abc/def/hij..).

How to Associate Operating System Files with a BFILE

To associate an operating system file to a BFILE, first create a DIRECTORY object which is an alias for the full path name to the operating system file.

To associate existing operating system files with relevant database records of a particular table use Oracle SQL DML (Data Manipulation Language). For example:

- Use INSERT to initialize a BFILE column to point to an existing file in the server file system

- Use UPDATE to change the reference target of the BFILE

- Initialize a BFILE to NULL and then update it later to refer to an operating system file using the BFILENAME function.

- OCI users can also use OCILobFileSetName() to initialize a BFILE locator variable that is then used in the VALUES clause of an INSERT statement.

Directory Example

The following statements associate the files Image1.gif and image2.gif with records having key_value of 21 and 22 respectively. 'IMG' is a DIRECTORY object that represents the physical directory under which Image1.gif and image2.gif are stored.

You may need to set up data structures similar to the following for certain examples to work:

CREATE TABLE Lob_table (
Key_value NUMBER NOT NULL,
F_lob BFILE)
INSERT INTO Lob_table VALUES
(21,  BFILENAME('IMG', 'Image1.gif'));
INSERT INTO Lob_table VALUES
(22, BFILENAME('IMG', 'image2.gif'));

The following UPDATE statement changes the target file to image3.gif for the row with key_value of 22.

UPDATE Lob_table SET f_lob = BFILENAME('IMG', 'image3.gif')
WHERE Key_value = 22;

Note:

The database does not expand environment variables specified in the DIRECTORY object or file name of a BFILE locator. For example, specifying:

BFILENAME('WORK_DIR', '$MY_FILE')

where MY_FILE, an environment variable defined in the operating system, is not valid.

BFILENAME and Initialization

BFILENAME is a built-in function that you use to initialize a BFILE column to point to an external file.

Once physical files are associated with records using SQL DML, subsequent read operations on the BFILE can be performed using PL/SQL DBMS_LOB package and OCI. However, these files are read-only when accessed through BFILEs, and so they cannot be updated or deleted through BFILEs.

As a consequence of the reference-based semantics for BFILEs, it is possible to have multiple BFILE columns in the same record or different records referring to the same file. For example, the following UPDATE statements set the BFILE column of the row with key_value =1 in lob_table to point to the same file as the row with key_value =22.

UPDATE lob_table
SET f_lob = (SELECT f_lob FROM lob_table WHERE key_value = 22)
WHERE key_value = 21;

Think of BFILENAME in terms of initialization — it can initialize the value for the following:

- BFILE column

- BFILE (automatic) variable declared inside a PL/SQL module

Characteristics of the BFILE Datatype

Using the BFILE datatype has the following advantages:

- If your need for a particular BFILE is temporary and limited within the module on which you are working, then you can use the BFILE related APIs on the variable without ever having to associate this with a column in the database.

- Because you are not forced to create a BFILE column in a server side table, initialize this column value, and then retrieve this column value using a SELECT, you save a round-trip to the server.

For more information, refer to the example given for DBMS_LOB.LOADFROMFILE (see "Loading a LOB with BFILE Data").

The OCI counterpart for BFILENAME is OCILobFileSetName(), which can be used in a similar fashion.

DIRECTORY Name Specification

You must have CREATE ANY DIRECTORY system privilege to create directories. Path names cannot contain two dots (".."). The naming convention for DIRECTORY objects is the same as that for tables and indexes. That is, normal identifiers are interpreted in uppercase, but delimited identifiers are interpreted as is. For example, the following statement:

CREATE OR REPLACE DIRECTORY scott_dir AS '/usr/home/scott';

creates or redefines a directory object whose name is 'SCOTT_DIR' (in uppercase). But if a delimited identifier is used for the DIRECTORY name, as shown in the following statement

CREATE DIRECTORY "Mary_Dir" AS '/usr/home/mary';

then the directory object name is 'Mary_Dir'. Use 'SCOTT_DIR' and 'Mary_Dir' when calling BFILENAME. For example:

BFILENAME('SCOTT_DIR', 'afile')
BFILENAME('Mary_Dir', 'afile')

On Windows Platforms

On Windows platforms the directory names are case-insensitive. Therefore the following two statements refer to the same directory:

CREATE DIRECTORY "big_cap_dir" AS "g:\data\source";

CREATE DIRECTORY "small_cap_dir" AS "G:\DATA\SOURCE";

BFILE Security

This section introduces the BFILE security model and associated SQL statements. The main SQL statements associated with BFILE security are:

- SQL DDL: CREATE and REPLACE or ALTER a DIRECTORY object

- SQL DML: GRANT and REVOKE the READ system and object privileges on DIRECTORY objects

Ownership and Privileges

The DIRECTORY object is a system owned object. For more information on system owned objects, see Oracle Database SQL Reference. Oracle Database supports two new system privileges, which are granted only to DBA:

- CREATE ANY DIRECTORY — for creating or altering the directory object creation

- DROP ANY DIRECTORY — for deleting the directory object

Read Permission on a DIRECTORY Object

READ permission on the DIRECTORY object enables you to read files located under that directory. The creator of the DIRECTORY object automatically earns the READ privilege.

If you have been granted the READ permission with GRANT option, then you may in turn grant this privilege to other users/roles and add them to your privilege domains.

Note:

The READ permission is defined only on the DIRECTORY object, not on individual files. Hence there is no way to assign different privileges to files in the same directory.

The physical directory that it represents may or may not have the corresponding operating system privileges (read in this case) for the Oracle Server process.

It is the responsibility of the DBA to ensure the following:

- That the physical directory exists

- Read permission for the Oracle Server process is enabled on the file, the directory, and the path leading to it

- The directory remains available, and read permission remains enabled, for the entire duration of file access by database users

The privilege just implies that as far as the Oracle Server is concerned, you may read from files in the directory. These privileges are checked and enforced by the PL/SQL DBMS_LOB package and OCI APIs at the time of the actual file operations.

Caution:

Because CREATE ANY DIRECTORY and DROP ANY DIRECTORY privileges potentially expose the server file system to all database users, the DBA should be prudent in granting these privileges to normal database users to prevent security breach.

SQL DDL for BFILE Security

Refer to the Oracle Database SQL Reference for information about the following SQL DDL statements that create, replace, and drop directory objects:

- CREATE DIRECTORY

- DROP DIRECTORY

SQL DML for BFILE Security

Refer to the Oracle Database SQL Reference for information about the following SQL DML statements that provide security for BFILEs:

- GRANT (system privilege)

- GRANT (object privilege)

- REVOKE (system privilege)

- REVOKE (object privilege)

- AUDIT (new statements)

- AUDIT (schema objects)

Catalog Views on Directories

Catalog views are provided for DIRECTORY objects to enable users to view object names and corresponding paths and privileges. Supported views are:

- ALL_DIRECTORIES (OWNER, DIRECTORY_NAME, DIRECTORY_PATH)

This view describes all directories accessible to the user.

- DBA_DIRECTORIES(OWNER, DIRECTORY_NAME, DIRECTORY_PATH)

This view describes all directories specified for the entire database.

Guidelines for DIRECTORY Usage

The main goal of the DIRECTORY feature is to enable a simple, flexible, non-intrusive, yet secure mechanism for the DBA to manage access to large files in the server file system. But to realize this goal, it is very important that the DBA follow these guidelines when using DIRECTORY objects:

- Do not map a DIRECTORY object to a data file directory. A DIRECTORY object should not be mapped to physical directories that contain Oracle data files, control files, log files, and other system files. Tampering with these files (accidental or otherwise) could corrupt the database or the server operating system.

- Only the DBA should have system privileges. The system privileges such as CREATE ANY DIRECTORY (granted to the DBA initially) should be used carefully and not granted to other users indiscriminately. In most cases, only the database administrator should have these privileges.

- Use caution when granting the DIRECTORY privilege. Privileges on DIRECTORY objects should be granted to different users carefully. The same holds for the use of the WITH GRANT OPTION clause when granting privileges to users.

- Do not drop or replace DIRECTORY objects when database is in operation. DIRECTORY objects should not be arbitrarily dropped or replaced when the database is in operation. If this were to happen, then operations from all sessions on all files associated with this directory object will fail. Further, if a DROP or REPLACE command is executed before these files could be successfully closed, then the references to these files will be lost in the programs, and system resources associated with these files will not be released until the session(s) is shut down.

The only recourse left to PL/SQL users, for example, will be to either run a program block that calls DBMS_LOB.FILECLOSEALL and restart their file operations, or exit their sessions altogether. Hence, it is imperative that you use these commands with prudence, and preferably during maintenance downtimes.

- Use caution when revoking a user's privilege on DIRECTORY objects. Revoking a user's privilege on a DIRECTORY object using the REVOKE statement causes all subsequent operations on dependent files from the user's session to fail. Either you must re-acquire the privileges to close the file, or run a FILECLOSEALL in the session and restart the file operations.

In general, using DIRECTORY objects for managing file access is an extension of system administration work at the operating system level. With some planning, files can be logically organized into suitable directories that have READ privileges for the Oracle process.

DIRECTORY objects can be created with READ privileges that map to these physical directories, and specific database users granted access to these directories.

BFILEs in Shared Server (Multithreaded Server) Mode

The database does not support session migration for BFILE datatypes in shared server (multithreaded server) mode. This implies that operations on open BFILE instances can persist beyond the end of a call to a shared server.

In shared server sessions, BFILE operations will be bound to one shared server, they cannot migrate from one server to another. This restriction will be removed in a forthcoming release.

External LOB (BFILE) Locators

For BFILEs, the value is stored in a server-side operating system file; in other words, external to the database. The BFILE locator that refers to that file is stored in the row.

When Two Rows in a BFILE Table Refer to the Same File

If a BFILE locator variable that is used in a DBMS_LOB.FILEOPEN (for example L1) is assigned to another locator variable, (for example L2), then both L1 and L2 point to the same file. This means that two rows in a table with a BFILE column can refer to the same file or to two distinct files — a fact that the canny developer might turn to advantage, but which could well be a pitfall for the unwary.

BFILE Locator Variable

A BFILE locator variable operates like any other automatic variable. With respect to file operations, it operates like a file descriptor available as part of the standard input/output library of most conventional programming languages. This implies that once you define and initialize a BFILE locator, and open the file pointed to by this locator, all subsequent operations until the closure of this file must be done from within the same program block using this locator or local copies of this locator.

Guidelines for BFILEs

Note the following guidelines when working with BFILEs:

- Open and close a file from the same program block at same nesting level. The BFILE locator variable can be used, just as any scalar, as a parameter to other procedures, member methods, or external function callouts. However, it is recommended that you open and close a file from the same program block at the same nesting level.

- Set the BFILE value before flushing the object to the database. If an object contains a BFILE, then you must set the BFILE value before flushing the object to the database, thereby inserting a new row. In other words, you must call OCILobFileSetName() after OCIObjectNew() and before OCIObjectFlush().

- Indicate the DIRECTORY object name and file name before inserting or updating of a BFILE. It is an error to insert or update a BFILE without indicating a directory object name and file name.

This rule also applies to users using an OCI bind variable for a BFILE in an insert or update statement. The OCI bind variable must be initialized with a directory object name and file name before issuing the insert or update statement.

- Initialize BFILE Before insert or update

Note:

OCISetAttr() does not allow the user to set a BFILE locator to NULL.

- Before using SQL to insert or update a row with a BFILE, you must initialize the BFILE to one of the following:

- NULL (not possible if using an OCI bind variable)

- A directory object name and file name

- A path name cannot contain two dots ("..") anywhere in its specification. A file name cannot start with two dots.

Loading a LOB with BFILE Data

This section describes how to load a LOB with data from a BFILE.

See Also:

Table 15-1, "Environments Supported for BFILE APIs", for a list of operations on BFILEs and APIs provided for each programmatic environment.

Preconditions

The following preconditions must exist before calling this procedure:

- The source BFILE instance must exist.

- The destination LOB instance must exist.

Usage Notes

Note:

The LOADBLOBFROMFILE and LOADCLOBFROMFILE procedures implement the functionality of this procedure and provide improved features for loading binary data and character data. The improved procedures are available in the PL/SQL environment only. When possible, using one of the improved procedures is recommended. See "Loading a BLOB with Data from a BFILE" and "Loading a CLOB or NCLOB with Data from a BFILE" for more information.

Character Set Conversion

In using OCI, or any of the programmatic environments that access OCI functionality, character set conversions are implicitly performed when translating from one character set to another.

BFILE to CLOB or NCLOB: Converting From Binary Data to a Character Set

When you use the DBMS_LOB.LOADFROMFILE procedure to populate a CLOB or NCLOB, you are populating the LOB with binary data from the BFILE. No implicit translation is performed from binary data to a character set. For this reason, you should use the LOADCLOBFROMFILE procedure when loading text (see Loading a CLOB or NCLOB with Data from a BFILE).

See Also:

Oracle Database Globalization Support Guide for character set conversion issues.

Amount Parameter

Note the following with respect to the amount parameter:

- DBMS_LOB.LOADFROMFILE

If you want to load the entire BFILE, then pass the constant DBMS_LOB.LOBMAXSIZE. If you pass any other value, then it must be less than or equal to the size of the BFILE.

- OCILobLoadFromFile()

If you want to load the entire BFILE, then you can pass the constant UB4MAXVAL. If you pass any other value, then it must be less than or equal to the size of the BFILE.

- OCILobLoadFromFile2()

If you want to load the entire BFILE, then you can pass the constant UB8MAXVAL. If you pass any other value, then it must be less than or equal to the size of the BFILE.

See Also:

Table 14-2, "Maximum LOB Size for Load from File Operations" for details on the maximum value of the amount parameter.

Syntax

Use the following syntax references for each programmatic environment:

- PL/SQL (DBMS_LOB) (Oracle Database PL/SQL Packages and Types Reference): "DBMS_LOB" — LOADFROMFILE

- C (OCI): Oracle Call Interface Programmer's Guide): Chapter 7, "LOB and File Operations", for usage notes and examples. Chapter 16, "LOB Functions" — OCILobLoadFromFile2().

- COBOL (Pro*COBOL) Pro*COBOL Programmer's Guide for information on LOBs, usage notes on LOB Statements, embedded SQL, and LOB LOAD precompiler directives.

- C/C++ (Pro*C/C++) (Pro*C/C++ Programmer's Guide): "Large Objects (LOBs)", "LOB Statements" "Embedded SQL Statements and Directives"— LOB LOAD.

- Visual Basic (OO4O) (Oracle Objects for OLE (OO4O) Online Help): From Help Topics, Contents tab, select OO4O Automation Server > OBJECTS > OraBLOB.OraCLOB > METHODS > CopyFromBfile

- Java (JDBC) Oracle Database JDBC Developer's Guide and Reference): "Working With LOBs" — Creating and Populating a BLOB or CLOB Column.

Examples

Examples are provided in the following programmatic environments:

- PL/SQL (DBMS_LOB): floaddat.sql

- OCI: floaddat.c

- Visual Basic (OO4O): floaddat.bas

- Java (JDBC): No example.

Opening a BFILE with OPEN

This section describes how to open a BFILE using the OPEN function.

Note:

You can also open a BFILE using the FILEOPEN function; however, using the OPEN function is recommended for new development. Using the FILEOPEN function is described in Opening a BFILE with FILEOPEN.

See Also:

Table 15-1, "Environments Supported for BFILE APIs", for a list of operations on BFILEs and APIs provided for each programmatic environment.

Syntax

Use the following syntax references for each programmatic environment:

- PL/SQL(DBMS_LOB) (Oracle Database PL/SQL Packages and Types Reference): "DBMS_LOB" — OPEN

- C (OCI) (Oracle Call Interface Programmer's Guide): Chapter 7, "LOB and File Operations", for usage notes. Chapter 16, section "LOB Functions" — OCILobOpen(), OCILobClose().

- COBOL (Pro*COBOL) Pro*COBOL Programmer's Guide for information on LOBs, usage notes on LOB statements, and embedded SQL and precompiler directives — LOB OPEN.

- C/C++ (Pro*C/C++) (Pro*C/C++ Programmer's Guide): "Large Objects (LOBs)", "LOB Statements", "Embedded SQL Statements and Directives" — LOB OPEN.

- Visual Basic (OO4O) (Oracle Objects for OLE (OO4O) Online Help): From Help Topics, Contents tab, select OO4O Automation Server > OBJECTS > OraBfile > METHODS > Open, and > OBJECTS > OraDynaset > METHODS > MoveFirst MoveLast MovePrevious MoveNext

- Java (JDBC) (Oracle Database JDBC Developer's Guide and Reference): "Working With LOBs" — Creating and Populating a BLOB or CLOB Column.

Scenario

These examples open an image in operating system file ADPHOTO_DIR.

Examples

Examples are provided in the following six programmatic environments:

- PL/SQL(DBMS_LOB): fopen.sql

- OCI: fopen.c

- Visual Basic (OO4O): fopen.bas

- Java (JDBC): fopen.java

Opening a BFILE with FILEOPEN

This section describes how to open a BFILE using the FILEOPEN function.

Note:

The FILEOPEN function is not recommended for new application development. The OPEN function is recommended for new development. See "Opening a BFILE with OPEN"

See Also:

Table 15-1, "Environments Supported for BFILE APIs", for a list of operations on BFILEs and APIs provided for each programmatic environment.

Usage Notes for Opening a BFILE

While you can continue to use the older FILEOPEN form, Oracle strongly recommends that you switch to using OPEN, because this facilitates future extensibility.

Syntax

Use the following syntax references for each programmatic environment:

- PL/SQL (DBMS_LOB) (Oracle Database PL/SQL Packages and Types Reference): "DBMS_LOB" — FILEOPEN, FILECLOSE

- C (OCI) (Oracle Call Interface Programmer's Guide): Chapter 7, "LOB and File Operations, for usage notes. Chapter 16, section "LOB Functions" — OCILobFileOpen(), OCILobFileClose(), OCILobFileSetName().

- COBOL (Pro*COBOL): A syntax reference is not applicable in this release.

- C/C++ (Pro*C/C++): A syntax reference is not applicable in this release.

- Visual Basic (OO4O): A syntax reference is not applicable in this release.

- Java (JDBC) (Oracle Database JDBC Developer's Guide and Reference): Chapter 7, "Working With LOBs" — Creating and Populating a BLOB or CLOB Column.

Scenario for Opening a BFILE

These examples open keyboard_logo.jpg in directory object MEDIA_DIR.

Examples

Examples are provided in the following four programmatic environments:

- PL/SQL (DBMS_LOB): ffilopen.sql

- OCI: ffilopen.c

- Java (JDBC): ffilopen.java

Determining Whether a BFILE Is Open Using ISOPEN

This section describes how to determine whether a BFILE is open using ISOPEN.

Note:

This function (ISOPEN) is recommended for new application development. The older FILEISOPEN function, described in "Determining Whether a BFILE Is Open with FILEISOPEN", is not recommended for new development.

See Also:

Table 15-1, "Environments Supported for BFILE APIs", for a list of operations on BFILEs and APIs provided for each programmatic environment.

Syntax

Use the following syntax references for each programmatic environment:

- PL/SQL (DBMS_LOB) (Oracle Database PL/SQL Packages and Types Reference): "DBMS_LOB" — ISOPEN

- C (OCI) (Oracle Call Interface Programmer's Guide): Chapter 7, "LOB and File Operations" for usage notes. Chapter 16, section "LOB Functions" — OCILobFileIsOpen().

- COBOL (Pro*COBOL) Pro*COBOL Programmer's Guide for information on LOBs, usage notes on LOB Statements, and embedded SQL and precompiler directives — LOB DESCRIBE ... ISOPEN.

- C/C++ (Pro*C/C++) (Pro*C/C++ Programmer's Guide): "Large Objects (LOBs)", "LOB Statements", "Large Objects (LOBs)", "LOB Statements", "Embedded SQL Statements and Directives" — LOB DESCRIBE ... ISOPEN

- Visual Basic (OO4O) (Oracle Objects for OLE (OO4O) Online Help): From Help Topics, Contents tab, select OO4O Automation Server > OBJECTS > OraBfile > METHODS > IsOpen and > OBJECTS > OraDynaset

- Java (JDBC) (Oracle Database JDBC Developer's Guide and Reference): "Working With LOBs" — Creating and Populating a BLOB or CLOB Column.

Examples

Examples are provided in the following six programmatic environments:

- PL/SQL (DBMS_LOB): fisopen.sql

- OCI: fisopen.c

- Visual Basic (OO4O): fisopen.bas

- Java (JDBC): fisopen.java

Determining Whether a BFILE Is Open with FILEISOPEN

This section describes how to determine whether a BFILE is OPEN using the FILEISOPEN function.

Note:

The FILEISOPEN function is not recommended for new application development. The ISOPEN function is recommended for new development. See Determining Whether a BFILE Is Open Using ISOPEN

See Also:

Table 15-1, "Environments Supported for BFILE APIs", for a list of operations on BFILEs and APIs provided for each programmatic environment.

Usage Notes

While you can continue to use the older FILEISOPEN form, Oracle strongly recommends that you switch to using ISOPEN, because this facilitates future extensibility.

Syntax

Use the following syntax references for each programmatic environment:

- PL/SQL(DBMS_LOB) (Oracle Database PL/SQL Packages and Types Reference): "DBMS_LOB" — FILEISOPEN

- C (OCI) (Oracle Call Interface Programmer's Guide): Chapter 7, "LOB and File Operations" for usage notes. Chapter 16, section "LOB Functions" — OCILobFileIsOpen().

- COBOL (Pro*COBOL): A syntax reference is not applicable in this release.

- C/C++ (Pro*C/C++): A syntax reference is not applicable in this release.

- Visual Basic (OO4O): A syntax reference is not applicable in this release.

- Java (JDBC) (Oracle Database JDBC Developer's Guide and Reference): "Working With LOBs" — Creating and Populating a BLOB or CLOB Column.

Scenario

These examples query whether a BFILE associated with ad_graphic is open.

Examples

Examples are provided in the following programmatic environments:

- PL/SQL(DBMS_LOB): ffisopen.sql

- OCI: ffisopen.c

- Java (JDBC): ffisopen.java

Displaying BFILE Data

This section describes how to display BFILE data.

See Also:

Table 15-1, "Environments Supported for BFILE APIs", for a list of operations on BFILEs and APIs provided for each programmatic environment.

Syntax

Use the following syntax references for each programmatic environment:

- PL/SQL (DBMS_LOB) (Oracle Database PL/SQL Packages and Types Reference): "DBMS_LOB" — READ. Chapter 29, "DBMS_OUTPUT" - PUT_LINE

- C (OCI) (Oracle Call Interface Programmer's Guide): Chapter 7, "LOB and File Operations" for usage notes. Chapter 16, section "LOB Functions" — OCILobFileOpen(), OCILobRead2().

- COBOL (Pro*COBOL) Pro*COBOL Programmer's Guide for information on LOBs, usage notes on LOB Statements, and embedded SQL and precompiler directives — LOB READ, DISPLAY.

- C/C++ (Pro*C/C++) (Pro*C/C++ Programmer's Guide): "Large Objects (LOBs)", "LOB Statements" — READ

- Visual Basic (OO4O) (Oracle Objects for OLE (OO4O) Online Help): From Help Topics, Contents tab, select OO4O Automation Server > OBJECTS > OraBFILE > METHODS > Read, and OO4O Automation Server > OBJECTS > OraBFILE > PROPERTIES > PollingAmount, Offset, Status. See also OO4O Automation Server > OBJECTS > OraBFILE > Examples

- Java (JDBC) (Oracle Database JDBC Developer's Guide and Reference): Chapter 7, "Working With LOBs" — Creating and Populating a BLOB or CLOB Column.

Examples

Examples are provided in six programmatic environments:

- PL/SQL (DBMS_LOB): fdisplay.sql

- OCI: fdisplay.c

- Java (JDBC): fdisplay.java

Reading Data from a BFILE

This section describes how to read data from a BFILE.

See Also:

Table 15-1, "Environments Supported for BFILE APIs", for a list of operations on BFILEs and APIs provided for each programmatic environment.

Usage Notes

Note the following when using this operation.

Streaming Read in OCI

The most efficient way to read large amounts of BFILE data is by OCILobRead2() with the streaming mechanism enabled, and using polling or callback. To do so, specify the starting point of the read using the offset parameter as follows:

ub8  char_amt =  0;
ub8  byte_amt =  0;
ub4  offset = 1000;

OCILobRead2(svchp, errhp, locp, &byte_amt, &char_amt, offset, bufp, bufl,
OCI_ONE_PIECE, 0, 0, 0, 0);

When using polling mode, be sure to look at the value of the byte_amt parameter after each OCILobRead2() call to see how many bytes were read into the buffer, because the buffer may not be entirely full.

When using callbacks, the lenp parameter, which is input to the callback, will indicate how many bytes are filled in the buffer. Be sure to check the lenp parameter during your callback processing because the entire buffer may not be filled with data (see the Oracle Call Interface Programmer's Guide.)

Amount Parameter

- When calling DBMS_LOB.READ, the amount parameter can be larger than the size of the data; however, the amount parameter should be less than or equal to the size of the buffer. In PL/SQL, the buffer size is limited to 32K.

- When calling OCILobRead2(), you can pass a value of 0 (zero) for the byte_amt parameter to read to the end of the BFILE.

Syntax

Use the following syntax references for each programmatic environment:

- PL/SQL (DBMS_LOB) (Oracle Database PL/SQL Packages and Types Reference): "DBMS_LOB" — READ

- C (OCI) (Oracle Call Interface Programmer's Guide): Chapter 7, "LOB and File Operations" for usage notes. Chapter 16, section "LOB Functions" — OCILobRead2().

- COBOL (Pro*COBOL) Pro*COBOL Programmer's Guide for information on LOBs, usage notes on LOB Statements, and embedded SQL and precompiler directives — LOB READ.

- C/C++ (Pro*C/C++) (Pro*C/C++ Programmer's Guide): "Large Objects (LOBs)", "LOB Statements", "Embedded SQL Statements and Directives" — LOB READ

- Visual Basic (OO4O) (Oracle Objects for OLE (OO4O) Online Help): From Help Topics, Contents tab, select OO4O Automation Server > OBJECTS > OraBFILE > METHODS > Read, and OO4O Automation Server > OBJECTS > OraBFILE > PROPERTIES > PollingAmount, Offset, Status. See also OO4O Automation Server > OBJECTS > OraBFILE > Examples

- Java (JDBC) (Oracle Database JDBC Developer's Guide and Reference): Chapter 7, "Working With LOBs" — Creating and Populating a BLOB or CLOB Column.

Examples

Examples are provided in the following programmatic environments:

- PL/SQL (DBMS_LOB): fread.sql

- OCI: fread.c

- Visual Basic (OO4O): fread.bas

- Java (JDBC): fread.java

Reading a Portion of BFILE Data Using SUBSTR

This section describes how to read portion of BFILE data using SUBSTR.

See Also:

Table 15-1, "Environments Supported for BFILE APIs", for a list of operations on BFILEs and APIs provided for each programmatic environment.

Syntax

Use the following syntax references for each programmatic environment:

- PL/SQL (DBMS_LOB) (Oracle Database PL/SQL Packages and Types Reference): "DBMS_LOB" — SUBSTR

- OCI: A syntax reference is not applicable in this release.

- COBOL (Pro*COBOL) Pro*COBOL Programmer's Guide for information on LOBs, usage notes on LOB Statements, and embedded SQL and precompiler directives — LOB OPEN, LOB CLOSE. See PL/SQL DBMS_LOB.SUBSTR.

- C/C++ (Pro*C/C++) (Pro*C/C++ Programmer's Guide): "Large Objects (LOBs)", "LOB Statements", "Embedded SQL Statements and Directives" — LOB OPEN. See also PL/SQL DBMS_LOB.SUBSTR

- Visual Basic (OO4O) (Oracle Objects for OLE (OO4O) Online Help): From Help Topics, Contents tab, select OO4O Automation Server > OBJECTS > OraBFILE > METHODS > Open, and OO4O Automation Server > OBJECTS > OraBFILE > PROPERTIES > PollingAmount, Offset, Status. See also OO4O Automation Server > OBJECTS > OraBFILE > Examples

- Java (JDBC) (Oracle Database JDBC Developer's Guide and Reference): Chapter 7, "Working With LOBs" — Creating and Populating a BLOB or CLOB Column.

Examples

Examples are provided in these five programmatic environments:

- PL/SQL (DBMS_LOB): freadprt.sql

- C (OCI): No example is provided with this release.

- Visual Basic (OO4O): freadprt.bas

- Java (JDBC): freadprt.java

Comparing All or Parts of Two BFILES

This section describes how to compare all or parts of two BFILEs.

See Also:

Table 15-1, "Environments Supported for BFILE APIs", for a list of operations on BFILEs and APIs provided for each programmatic environment.

Syntax

Use the following syntax references for each programmatic environment:

- PL/SQL(DBMS_LOB) (Oracle Database PL/SQL Packages and Types Reference): "DBMS_LOB" — COMPARE

- C (OCI): A syntax reference is not applicable in this release.

- COBOL (Pro*COBOL) Pro*COBOL Programmer's Guide for information on LOBs, usage notes on LOB Statements, and embedded SQL and precompiler directives — LOB OPEN. See PL/SQL DBMS_LOB.COMPARE.

- C/C++ (Pro*C/C++) (Pro*C/C++ Programmer's Guide): "Large Objects (LOBs)", "LOB Statements", "Embedded SQL Statements and Directives" — LOB OPEN. See PL/SQL DBMS_LOB.COMPARE.

- Visual Basic (OO4O) (Oracle Objects for OLE (OO4O) Online Help): From Help Topics, Contents tab, select OO4O Automation Server > OBJECTS > OraBFILE > METHODS > Open, Compare, and OO4O Automation Server > OBJECTS > OraDatabase > PROPERTIES > Parameters. See also OO4O Automation Server > OBJECTS > OraBFILE > Examples

- Java (JDBC) (Oracle Database JDBC Developer's Guide and Reference): Chapter 7, "Working With LOBs" — Creating and Populating a BLOB or CLOB Column.

Examples

Examples are provided in these five programmatic environments:

- PL/SQL(DBMS_LOB): fcompare.sql

- OCI: No example is provided with this release.

- Visual Basic (OO4O): fcompare.bas

- Java (JDBC): fcompare.java

Checking If a Pattern Exists in a BFILE Using INSTR

This section describes how to determine whether a pattern exists in a BFILE using INSTR.

See Also:

Table 15-1, "Environments Supported for BFILE APIs", for a list of operations on BFILEs and APIs provided for each programmatic environment.

Syntax

Use the following syntax references for each programmatic environment:

- PL/SQL (DBMS_LOB) (Oracle Database PL/SQL Packages and Types Reference): "DBMS_LOB" — INSTR

- C (OCI): A syntax reference is not applicable in this release.

- COBOL (Pro*COBOL) Pro*COBOL Programmer's Guide for information on LOBs, usage notes on LOB Statements, and embedded SQL and precompiler directives — LOB OPEN. See PL/SQL DBMS_LOB.INSTR.

- C/C++ (Pro*C/C++) (Pro*C/C++ Programmer's Guide): "Large Objects (LOBs)", "LOB Statements", "Embedded SQL Statements and Directives" — LOB OPEN. See PL/SQL DBMS_LOB.INSTR.

- Visual Basic (OO4O): A syntax reference is not applicable in this release.

- Java (JDBC) (Oracle Database JDBC Developer's Guide and Reference): Chapter 7, "Working With LOBs" — Creating and Populating a BLOB or CLOB Column.

Examples

These examples are provided in the following four programmatic environments:

- PL/SQL (DBMS_LOB): fpattern.sql

- OCI: No example is provided with this release.

- Visual Basic (OO4O): No example is provided with this release.

- Java (JDBC): fpattern.java

Determining Whether a BFILE Exists

This procedure determines whether a BFILE locator points to a valid BFILE instance.

See Also:

Table 15-1, "Environments Supported for BFILE APIs", for a list of operations on BFILEs and APIs provided for each programmatic environment.

Syntax

Use the following syntax references for each programmatic environment:

- PL/SQL (DBMS_LOB) Oracle Database PL/SQL Packages and Types Reference): "DBMS_LOB" — FILEEXISTS

- C (OCI) Oracle Call Interface Programmer's Guide): Chapter 7, "LOB and File Operations" for usage notes. Chapter 16, section "LOB Functions" — OCILobFileExists().

- COBOL (Pro*COBOL) Pro*COBOL Programmer's Guide for information on LOBs, usage notes on LOB Statements, and embedded SQL and precompiler directives — LOB DESCRIBE ... FILEEXISTS.

- C/C++ (Pro*C/C++) Pro*C/C++ Programmer's Guide): "Large Objects (LOBs)", "LOB Statements", "Embedded SQL Statements and Directives" — LOB DESCRIBE ...GET FILEEXISTS

- Visual Basic (OO4O) (Oracle Objects for OLE (OO4O) Online Help): From Help Topics, Contents tab, select OO4O Automation Server > OBJECTS > OraBFILE > PROPERTIES > Exists, and OO4O Automation Server > OBJECTS > OraDatabase > PROPERTIES > Parameters. See also OO4O Automation Server > OBJECTS > OraBFILE > Examples

- Java (JDBC) Oracle Database JDBC Developer's Guide and Reference: "Working With LOBs" — Creating and Populating a BLOB or CLOB Column.

Examples

The examples are provided in the following six programmatic environments:

- PL/SQL (DBMS_LOB): fexists.sql

- OCI: fexists.c

- Visual Basic (OO4O): fexists.bas

- Java (JDBC): fexists.java

Getting the Length of a BFILE

This section describes how to get the length of a BFILE.

See Also:

Table 15-1, "Environments Supported for BFILE APIs", for a list of operations on BFILEs and APIs provided for each programmatic environment.

Syntax

Use the following syntax references for each programmatic environment:

- PL/SQL (DBMS_LOB) (Oracle Database PL/SQL Packages and Types Reference): "DBMS_LOB" — GETLENGTH

- C (OCI) (Oracle Call Interface Programmer's Guide): Chapter 7, "LOB and File Operations". Chapter 16, section "LOB Functions" — OCILobGetLength2().

- COBOL (Pro*COBOL) Pro*COBOL Programmer's Guide for information on LOBs, usage notes on LOB Statements, and embedded SQL and precompiler directives — LOB DESCRIBE ... GET LENGTH INTO ...

- C/C++ (Pro*C/C++) (Pro*C/C++ Programmer's Guide): "Large Objects (LOBs)", "LOB Statements", "Embedded SQL Statements and Directives" — LOB DESCRIBE ... GET LENGTH INTO ...

- Visual Basic (OO4O) (Oracle Objects for OLE (OO4O) Online Help): From Help Topics, Contents tab, select OO4O Automation Server > OBJECTS > OraBFILE > PROPERTIES > Size. See also OO4O Automation Server > OBJECTS > OraBfile > Examples

- Java (JDBC) Oracle Database JDBC Developer's Guide and Reference: "Working With LOBs" — Creating and Populating a BLOB or CLOB Column.

Examples

The examples are provided in six programmatic environments:

- PL/SQL (DBMS_LOB): flength.sql

- OCI: flength.c

- Visual Basic (OO4O): flength.bas

- Java (JDBC): flength.java

Assigning a BFILE Locator

This section describes how to assign one BFILE locator to another.

See Also:

Table 15-1, "Environments Supported for BFILE APIs", for a list of operations on BFILEs and APIs provided for each programmatic environment.

Syntax

Use the following syntax references for each programmatic environment:

- SQL (Oracle Database SQL Reference): Chapter 7, "SQL Statements" — CREATE PROCEDURE

- PL/SQL (DBMS_LOB): Refer to Chapter 5, "Advanced Design Considerations" of this manual for information on assigning one lob locator to another.

- C (OCI) (Oracle Call Interface Programmer's Guide): Chapter 7, "LOB and File Operations" for usage notes. Chapter 16, section "LOB Functions" — OCILobLocatorAssign().

- COBOL (Pro*COBOL) Pro*COBOL Programmer's Guide for information on LOBs, usage notes on LOB Statements, and embedded SQL and precompiler directives — LOB ASSIGN

- C/C++ (Pro*C/C++) (Pro*C/C++ Programmer's Guide): "Large Objects (LOBs)", "LOB Statements", "Embedded SQL Statements and Directives" — LOB ASSIGN

- Visual Basic (OO4O): A syntax reference is not applicable in this release.

- Java (JDBC) Oracle Database JDBC Developer's Guide and Reference: Chapter 7, "Working With LOBs" — Creating and Populating a BLOB or CLOB Column.

Examples

The examples are provided in the following five programmatic environments:

- PL/SQL (DBMS_LOB): fcopyloc.sql

- OCI: fcopyloc.c

- Visual Basic: An example is not provided with this release.

- Java (JDBC): fcopyloc.java

Getting Directory Object Name and File Name of a BFILE

This section describes how to get the directory object name and file name of a BFILE.

See Also:

Table 15-1, "Environments Supported for BFILE APIs", for a list of operations on BFILEs and APIs provided for each programmatic environment.

Syntax

Use the following syntax references for each programmatic environment:

- PL/SQL (DBMS_LOB) (Oracle Database PL/SQL Packages and Types Reference): "DBMS_LOB" — FILEGETNAME

- C (OCI) (Oracle Call Interface Programmer's Guide): Chapter 7, "LOB and File Operations" for usage notes. Chapter 16, section "LOB Functions" — OCILobFileGetName().

- COBOL (Pro*COBOL) Pro*COBOL Programmer's Guide for information on LOBs, usage notes on LOB Statements, and embedded SQL and precompiler directives — LOB DESCRIBE ...GET DIRECTORY ...

- C/C++ (Pro*C/C++) (Pro*C/C++ Programmer's Guide): "Large Objects (LOBs)", "LOB Statements", "Embedded SQL Statements and Directives" — LOB DESCRIBE ...GET DIRECTORY ...

- Java (JDBC) Oracle Database JDBC Developer's Guide and Reference: "Working With LOBs" — Creating and Populating a BLOB or CLOB Column.

Examples

Examples of this procedure are provided in the following programmatic environments:

- PL/SQL (DBMS_LOB): fgetdir.sql

- OCI: fgetdir.c

- Visual Basic (OO4O): fgetdir.bas

- Java (JDBC): fgetdir.java

Updating a BFILE by Initializing a BFILE Locator

This section describes how to update a BFILE by initializing a BFILE locator.

See Also:

Table 15-1, "Environments Supported for BFILE APIs", for a list of operations on BFILEs and APIs provided for each programmatic environment.

Syntax

Use the following syntax references for each programmatic environment:

- PL/SQL (DBMS_LOB): See the (Oracle Database SQL Reference), Chapter 7, "SQL Statements" — UPDATE

- C (OCI) (Oracle Call Interface Programmer's Guide): Chapter 7, "LOB and File Operations" for usage notes. Chapter 16, section "LOB Functions" — OCILobFileSetName().

- COBOL (Pro*COBOL) Pro*COBOL Programmer's Guide for information on LOBs, usage notes on LOB Statements, and embedded SQL and precompiler directives — ALLOCATE. See also (Oracle Database SQL Reference), Chapter 7, "SQL Statements" — UPDATE

- C/C++ (Pro*C/C++) (Pro*C/C++ Programmer's Guide): "Large Objects (LOBs)", "LOB Statements", "Embedded SQL Statements and Directives". See also (Oracle Database SQL Reference), Chapter 7, "SQL Statements" — UPDATE

- Visual Basic (OO4O) (Oracle Objects for OLE (OO4O) Online Help): From Help

- Topics, Contents tab, select OO4O Automation Server > OBJECTS > OraBFILE > PROPERTIES > DirectoryName, FileName, and OO4O Automation Server > OBJECTS > OraDatabase > METHODS > ExecuteSQL. See also OO4O Automation Server > OBJECTS > OraBfile > Examples

- Java (JDBC) Oracle Database JDBC Developer's Guide and Reference: Chapter 7, "Working With LOBs" — Creating and Populating a BLOB or CLOB Column.

Examples

The examples are provided in six programmatic environments:

- PL/SQL (DBMS_LOB): fupdate.sql

- OCI: fupdate.c

- Visual Basic (OO4O): fupdate.bas

- Java (JDBC): fupdate.java

Closing a BFILE with FILECLOSE

This section describes how to close a BFILE with FILECLOSE.

Note:

This function (FILECLOSE) is not recommended for new development. For new development, use the CLOSE function instead. See "Closing a BFILE with CLOSE" for more information.

See Also:

Table 15-1, "Environments Supported for BFILE APIs", for a list of operations on BFILEs and APIs provided for each programmatic environment.

Syntax

Use the following syntax references for each programmatic environment:

- PL/SQL (DBMS_LOB)(Oracle Database PL/SQL Packages and Types Reference): "DBMS_LOB" — FILEOPEN, FILECLOSE

- C (OCI) (Oracle Call Interface Programmer's Guide): Chapter 7, "LOB and File Operations" for usage notes. Chapter 16, section "LOB Functions" — OCILobFileClose().

- COBOL (Pro*COBOL): A syntax reference is not applicable in this release.

- C/C++ (Pro*C/C++): A syntax reference is not applicable in this release.

- Visual Basic (OO4O): A syntax reference is not applicable in this release.

- Java (JDBC) Oracle Database JDBC Developer's Guide and Reference: "Working With LOBs" — Creating and Populating a BLOB or CLOB Column.

Examples

- PL/SQL (DBMS_LOB): fclose_f.sql

- OCI: fclose_f.c

- Visual Basic (OO4O): This operation is not supported in Visual Basic. Instead use "Closing a BFILE with CLOSE" as described .

- Java (JDBC): fclose_f.java

Closing a BFILE with CLOSE

This section describes how to close a BFILE with the CLOSE function.

Note:

This function (CLOSE) is recommended for new application development. The older FILECLOSE function, is not recommended for new development.

See Also:

Table 15-1, "Environments Supported for BFILE APIs", for a list of operations on BFILEs and APIs provided for each programmatic environment.

Usage Notes

Opening and closing a BFILE is mandatory. You must close the instance later in the session.

See Also:

- Opening a BFILE with OPEN

- Determining Whether a BFILE Is Open Using ISOPEN

Syntax

Use the following syntax references for each programmatic environment:

- PL/SQL (DBMS_LOB) (Oracle Database PL/SQL Packages and Types Reference): "DBMS_LOB" — CLOSE

- C (OCI) (Oracle Call Interface Programmer's Guide): Chapter 7, "LOB and File Operations" for usage notes. Chapter 16, section "LOB Functions" — OCILobClose().

- COBOL (Pro*COBOL) Pro*COBOL Programmer's Guide for information on LOBs, usage notes on LOB Statements, and embedded SQL and precompiler directives — LOB CLOSE

- C/C++ (Pro*C/C++) (Pro*C/C++ Programmer's Guide): "Large Objects (LOBs)", "LOB Statements", "Embedded SQL Statements and Directives" — LOB CLOSE

- Visual Basic (OO4O) (Oracle Objects for OLE (OO4O) Online Help): From Help

- Topics, Contents tab, select OO4O Automation Server > OBJECTS > OraBFILE > PROPERTIES > IsOpen. See also OO4O Automation Server > OBJECTS > OraBFILE > Examples.

- Java (JDBC) Oracle Database JDBC Developer's Guide and Reference: "Working With LOBs" — Creating and Populating a BLOB or CLOB Column.

Examples

- PL/SQL (DBMS_LOB): fclose_c.sql

- OCI: fclose_c.c

- Visual Basic (OO4O): fclose_c.bas

- Java (JDBC): fclose_c.java

Closing All Open BFILEs with FILECLOSEALL

This section describes how to close all open BFILEs.

You are responsible for closing any BFILE instances before your program terminates. For example, you must close any open BFILE instance before the termination of a PL/SQL block or OCI program.

You must close open BFILE instances even in cases where an exception or unexpected termination of your application occurs. In these cases, if a BFILE instance is not closed, then it is still considered open by the database. Ensure that your exception handling strategy does not allow BFILE instances to remain open in these situations.

See Also:

- Table 15-1, "Environments Supported for BFILE APIs", for a list of operations on BFILEs and APIs provided for each programmatic environment.

- "Setting Maximum Number of Open BFILEs"

Syntax

Use the following syntax references for each programmatic environment:

- PL/SQL (DBMS_LOB) (Oracle Database PL/SQL Packages and Types Reference): "DBMS_LOB" — FILECLOSEALL

- C (OCI) (Oracle Call Interface Programmer's Guide): Chapter 7, "LOB and File Operations" for usage notes. Chapter 16, section "LOB Functions" — OCILobFileCloseAll().

- COBOL (Pro*COBOL) Pro*COBOL Programmer's Guide for information on LOBs, usage notes on LOB Statements, and embedded SQL and precompiler directives — LOB FILE CLOSE ALL

- C/C++ (Pro*C/C++) (Pro*C/C++ Programmer's Guide): "Large Objects (LOBs)", "LOB Statements", "Embedded SQL Statements and Directives" — LOB FILE CLOSE ALL

- Visual Basic (OO4O) (Oracle Objects for OLE (OO4O) Online Help): From Help Topics, Contents tab, select OO4O Automation Server > OBJECTS > OraBFILE > METHODS > CloseAll. See also OO4O Automation Server > OBJECTS > OraBFILE > Examples

- Java (JDBC) Oracle Database JDBC Developer's Guide and Reference: Chapter 7, "Working With LOBs" — Creating and Populating a BLOB or CLOB Column.

Examples

- PL/SQL (DBMS_LOB): fclosea.sql

- OCI: fclosea.c

- Visual Basic (OO4O): fclosea.bas

- Java (JDBC): fclosea.java

Inserting a Row Containing a BFILE

This section describes how to insert a row containing a BFILE by initializing a BFILE locator.

See Also:

- Table 15-1, "Environments Supported for BFILE APIs", for a list of operations on BFILEs and APIs provided for each programmatic environment.

Usage Notes

You must initialize the BFILE locator bind variable to NULL or a directory object and file name before issuing the INSERT statement.

Syntax

See the following syntax references for each programmatic environment:

- SQL(Oracle Database SQL Reference, Chapter 7 "SQL Statements" — INSERT

- C (OCI) Oracle Call Interface Programmer's Guide: Chapter 7, "LOB and File Operations".

- COBOL (Pro*COBOL) Pro*COBOL Programmer's Guide for information on LOBs, usage notes on LOB Statements, embedded SQL, and precompiler directives. See also Oracle Database SQL Reference, for related information on the SQL INSERT statement.

- C/C++ (Pro*C/C++) Pro*C/C++ Programmer's Guide: "Large Objects (LOBs)", "LOB Statements", "Embedded SQL Statements and Directives" — LOB FILE SET. See also (Oracle Database SQL Reference), Chapter 7 "SQL Statements" — INSERT

- Visual Basic (OO4O) (Oracle Objects for OLE (OO4O) Online Help): From Help Topics, Contents tab, select OO4O Automation Server > OBJECTS > OraBfile > METHODS > DirectoryName, FileName; and > OBJECTS > OraDynaset >

- METHODS > Update

- Java (JDBC) Oracle Database JDBC Developer's Guide and Reference: "Working With LOBs" — Creating and Populating a BLOB or CLOB Column.

Examples

Examples in the following programmatic environments are provided:

- PL/SQL (DBMS_LOB): finsert.sql

- OCI: finsert.c

- Visual Basic (OO4O): finsert.bas

- Java (JDBC): finsert.java

A LOB Demonstration Files

This appendix describes files distributed with the database that demonstrate how LOBs are used in supported programmatic environments. This appendix contains these topics:

- PL/SQL LOB Demonstration Files

- OCI LOB Demonstration Files

- Visual Basic OO4O LOB Demonstration Files

- Java LOB Demonstration Files

PL/SQL LOB Demonstration Files

The following table lists PL/SQL demonstration files. These files are installed in $ORACLE_HOME/rdbms/demo/lobs/plsql/. A driver program, lobdemo.sql, that calls these files is found in the same directory.

Table A-1 PL/SQL Demonstration Examples

File Name

Description

Usage Information

fclose_c.sql

Closing a BFILE with CLOSE

Closing a BFILE with CLOSE

fclose_f.sql

Closing a BFILE with FILECLOSE

Closing a BFILE with FILECLOSE

fclosea.sql

Closing all open BFILEs

Closing All Open BFILEs with FILECLOSEALL

fcompare.sql

Comparing all or parts of two BFILEs

Comparing All or Parts of Two BFILES

fcopyloc.sql

Copying a LOB locator for a BFILE

Assigning a BFILE Locator

fdisplay.sql

Displaying BFILE data

Displaying BFILE Data

fexists.sql

Checking if a BFILE exists

Determining Whether a BFILE Exists

ffilopen.sql

Opening a BFILE with FILEOPEN

Opening a BFILE with FILEOPEN

ffisopen.sql

Checking if the BFILE is OPEN with FILEISOPEN

Determining Whether a BFILE Is Open with FILEISOPEN

fgetdir.sql

Getting the directory object name and filename of a BFILE

Getting Directory Object Name and File Name of a BFILE

finsert.sql

Inserting row containing a BFILE by initializing a BFILE locator

Inserting a Row Containing a BFILE

fisopen.sql

Checking if the BFILE is open with ISOPEN

Determining Whether a BFILE Is Open Using ISOPEN

flength.sql

Getting the length of a BFILE

Getting the Length of a BFILE

floadlob.sql

Loading a LOB with BFILE data

Loading a LOB with BFILE Data

fopen.sql

Opening a BFILE with OPEN

Opening a BFILE with OPEN

fpattern.sql

Checking if a pattern exists in a BFILE using instr

Checking If a Pattern Exists in a BFILE Using INSTR

fread.sql

Reading data from a BFILE

Reading Data from a BFILE

freadprt.sql

Reading portion of a BFILE data using substr

Reading a Portion of BFILE Data Using SUBSTR

fupdate.sql

Updating a BFILE by initializing a BFILE locator

Updating a BFILE by Initializing a BFILE Locator

lappend.sql

Appending one LOB to another

Appending One LOB to Another

lcompare.sql

Comparing all or part of LOB

Comparing All or Part of Two LOBs

lcopy.sql

Copying all or part of a LOB to another LOB

Copying All or Part of One LOB to Another LOB

lcopyloc.sql

Copying a LOB locator

Copying All or Part of One LOB to Another LOB

ldisplay.sql

Displaying LOB data

Displaying LOB Data

lerase.sql

Erasing part of a LOB

Erasing Part of a LOB

linsert.sql

Inserting a row by initializing LOB locator bind variable

Inserting a Row by Initializing a LOB Locator Bind Variable

linstr.sql

Seeing if pattern exists in LOB (instr)

Patterns: Checking for Patterns in a LOB Using INSTR

lisopen.sql

Seeing if LOB is open

Determining Whether a LOB is Open

listemp.sql

Seeing if LOB is temporary

Determining Whether a LOB instance Is Temporary

lldblobf.sql

Using DBMS_LOB.LOADBLOBFROMFILE to load a BLOB with data from a BFILE

Loading a BLOB with Data from a BFILE

lldclobf.sql

Using DBMS_LOB.LOADCLOBFROMFILE to load a CLOB or NCLOB with data from a BFILE

Loading a CLOB or NCLOB with Data from a BFILE

lldclobs.sql

Using DBMS_LOB.LOADCLOBFROMFILE to load segments of a stream of data from a BFILE into different CLOBs

Loading a CLOB or NCLOB with Data from a BFILE

llength.sql

Getting the length of a LOB

Length: Determining the Length of a LOB

lloaddat.sql

Loading a LOB with BFILE data

Loading a LOB with Data from a BFILE

lobuse.sql

Examples of LOB API usage.

Creating Persistent and Temporary LOBs in PL/SQL

lread.sql

Reading data from LOB

Reading Data from a LOB

lsubstr.sql

Reading portion of LOB (substr)

Reading a Portion of a LOB (SUBSTR)

ltrim.sql

Trimming LOB data

Trimming LOB Data

lwrite.sql

Writing data to a LOB

Writing Data to a LOB

lwriteap.sql

Writing to the end of LOB (write append)

Appending to a LOB

OCI LOB Demonstration Files

The following table lists OCI demonstration files. These files are installed in $ORACLE_HOME/rdbms/demo/lobs/oci/. A driver program, lobdemo.c, that calls these files is found in the same directory, as is the header file lobdemo.h.

Table A-2 OCI Demonstration Examples

File Name

Description

Usage Information

fclose_c.c

Closing a BFILE with CLOSE

Closing a BFILE with CLOSE

fclose_f.c

Closing a BFILE with FILECLOSE

Closing a BFILE with FILECLOSE

fclosea.c

Closing all open BFILEs

Closing All Open BFILEs with FILECLOSEALL

fcopyloc.c

Copying a LOB locator for a BFILE

Assigning a BFILE Locator

fdisplay.c

Displaying BFILE data

Displaying BFILE Data

fexists.c

Checking if a BFILE exists

Determining Whether a BFILE Exists

ffilopen.c

Opening a BFILE with FILEOPEN

Opening a BFILE with FILEOPEN

ffisopen.c

Checking if the BFILE is OPEN with FILEISOPEN

Determining Whether a BFILE Is Open with FILEISOPEN

fgetdir.c

Getting the directory object name and filename of a BFILE

Getting Directory Object Name and File Name of a BFILE

finsert.c

Inserting row containing a BFILE by initializing a BFILE locator

Inserting a Row Containing a BFILE

fisopen.c

Checking if the BFILE is open with ISOPEN

Determining Whether a BFILE Is Open Using ISOPEN

flength.c

Getting the length of a BFILE

Getting the Length of a BFILE

floadlob.c

Loading a LOB with BFILE data

Loading a LOB with BFILE Data

fopen.c

Opening a BFILE with OPEN

Opening a BFILE with OPEN

fread.c

Reading data from a BFILE

Reading Data from a BFILE

fupdate.c

Updating a BFILE by initializing a BFILE locator

Updating a BFILE by Initializing a BFILE Locator

lappend.c

Appending one LOB to another

Appending One LOB to Another

lcopy.c

Copying all or part of a LOB to another LOB

Copying All or Part of One LOB to Another LOB

lcopyloc.c

Copying a LOB locator

Copying All or Part of One LOB to Another LOB

ldisbuf.c

Disabling LOB buffering (persistent LOBs)

Disabling LOB Buffering

ldisplay.c

Displaying LOB data

Displaying LOB Data

lequal.c

Seeing if one LOB locator is equal to another

Equality: Checking If One LOB Locator Is Equal to Another

lerase.c

Erasing part of a LOB

Erasing Part of a LOB

lgetchar.c

Getting character set id

Determining Character Set ID

lgetchfm.c

Getting character set form of the foreign language ad text, ad_fltextn

Determining Character Set Form

linit.c

Seeing if a LOB locator is initialized

Determining Whether LOB Locator Is Initialized

linsert.c

Inserting a row by initializing LOB locator bind variable

Inserting a Row by Initializing a LOB Locator Bind Variable

lisopen.c

Seeing if LOB is open

Determining Whether a LOB is Open

listemp.c

Seeing if LOB is temporary

Determining Whether a LOB instance Is Temporary

llength.c

Getting the length of a LOB

Length: Determining the Length of a LOB

lloaddat.c

Loading a LOB with BFILE data

Loading a LOB with Data from a BFILE

lread.c

Reading data from LOB

Reading Data from a LOB

lreadarr.c

Reading data from an array of LOB locators

LOB Array Read

ltrim.c

Trimming LOB data

Trimming LOB Data

lwrite.c

Writing data to a LOB

Writing Data to a LOB

lwritearr.c

Writing data into an array of LOB locators

LOB Array Write

lwriteap.c

Writing to the end of LOB (write append)

Appending to a LOB

Visual Basic OO4O LOB Demonstration Files

The following table lists Visual Basic OO4O demonstration files. These files are installed in $ORACLE_HOME/rdbms/demo/lobs/vb/.

Table A-3 Visual Basic OO4O Demonstration Examples

File Name

Description

Usage Information

fclose_c.bas

Closing a BFILE with CLOSE

Closing a BFILE with CLOSE

fclosea.bas

Closing all open BFILEs

Closing All Open BFILEs with FILECLOSEALL

fcompare.bas

Comparing all or parts of two BFILEs

Comparing All or Parts of Two BFILES

fdisplay.bas

Displaying BFILE data

Displaying BFILE Data

fexists.bas

Checking if a BFILE exists

Determining Whether a BFILE Exists

fgetdir.bas

Getting the directory object name and filename of a BFILE

Getting Directory Object Name and File Name of a BFILE

finsert.bas

Inserting row containing a BFILE by initializing a BFILE locator

Inserting a Row Containing a BFILE

fisopen.bas

Checking if the BFILE is open with ISOPEN

Determining Whether a BFILE Is Open Using ISOPEN

flength.bas

Getting the length of a BFILE

Getting the Length of a BFILE

floadlob.bas

Loading a LOB with BFILE data

Loading a LOB with BFILE Data

fopen.bas

Opening a BFILE with OPEN

Opening a BFILE with OPEN

fread.bas

Reading data from a BFILE

Reading Data from a BFILE

freadprt.bas

Reading portion of a BFILE data using substr

Reading a Portion of BFILE Data Using SUBSTR

fupdate.bas

Updating a BFILE by initializing a BFILE locator

Updating a BFILE by Initializing a BFILE Locator

lappend.bas

Appending one LOB to another

Appending One LOB to Another

lcompare.bas

Comparing all or part of LOB

Comparing All or Part of Two LOBs

lcopy.bas

Copying all or part of a LOB to another LOB

Copying All or Part of One LOB to Another LOB

lcopyloc.bas

Copying a LOB locator

Copying All or Part of One LOB to Another LOB

ldisbuf.bas

Disabling LOB buffering (persistent LOBs)

Disabling LOB Buffering

ldisplay.bas

Displaying LOB data

Displaying LOB Data

lenbuf.bas

Enabling LOB buffering

Enabling LOB Buffering

lerase.bas

Erasing part of a LOB

Erasing Part of a LOB

linsert.bas

Inserting a row by initializing LOB locator bind variable

Inserting a Row by Initializing a LOB Locator Bind Variable

llength.bas

Getting the length of a LOB

Length: Determining the Length of a LOB

lloaddat.bas

Loading a LOB with BFILE data

Loading a LOB with Data from a BFILE

lread.bas

Reading data from LOB

Reading Data from a LOB

lsubstr.bas

Reading portion of LOB (substr)

Reading a Portion of a LOB (SUBSTR)

ltrim.bas

Trimming LOB data

Trimming LOB Data

lwrite.bas

Writing data to a LOB

Writing Data to a LOB

Java LOB Demonstration Files

The following table lists Java demonstration files. These files are installed in $ORACLE_HOME/rdbms/demo/lobs/java/.

Table A-4 Java Demonstration Examples

File Name

Description

Usage Information

fclose_c.java

Closing a BFILE with CLOSE

Closing a BFILE with CLOSE

fclose_f.java

Closing a BFILE with FILECLOSE

Closing a BFILE with FILECLOSE

fclosea.java

Closing all open BFILEs

Closing All Open BFILEs with FILECLOSEALL

fcompare.java

Comparing all or parts of two BFILEs

Comparing All or Parts of Two BFILES

fcopyloc.java

Copying a LOB locator for a BFILE

Assigning a BFILE Locator

fdisplay.java

Displaying BFILE data

Displaying BFILE Data

fexists.java

Checking if a BFILE exists

Determining Whether a BFILE Exists

ffilopen.java

Opening a BFILE with FILEOPEN

Opening a BFILE with FILEOPEN

ffisopen.java

Checking if the BFILE is OPEN with FILEISOPEN

Determining Whether a BFILE Is Open with FILEISOPEN

fgetdir.java

Getting the directory object name and filename of a BFILE

Getting Directory Object Name and File Name of a BFILE

finsert.java

Inserting row containing a BFILE by initializing a BFILE locator

Inserting a Row Containing a BFILE

fisopen.java

Checking if the BFILE is open with ISOPEN

Determining Whether a BFILE Is Open Using ISOPEN

flength.java

Getting the length of a BFILE

Getting the Length of a BFILE

fopen.java

Opening a BFILE with OPEN

Opening a BFILE with OPEN

fpattern.java

Checking if a pattern exists in a BFILE using instr

Checking If a Pattern Exists in a BFILE Using INSTR

fread.java

Reading data from a BFILE

Reading Data from a BFILE

freadprt.java

Reading portion of a BFILE data using substr

Reading a Portion of BFILE Data Using SUBSTR

fupdate.java

Updating a BFILE by initializing a BFILE locator

Updating a BFILE by Initializing a BFILE Locator

lappend.java

Appending one LOB to another

Appending One LOB to Another

lcompare.java

Comparing all or part of LOB

Comparing All or Part of Two LOBs

lcopy.java

Copying all or part of a LOB to another LOB

Copying All or Part of One LOB to Another LOB

lcopyloc.java

Copying a LOB locator

Copying All or Part of One LOB to Another LOB

ldisplay.java

Displaying LOB data

Displaying LOB Data

lequal.java

Seeing if one LOB locator is equal to another

Equality: Checking If One LOB Locator Is Equal to Another

lerase.java

Erasing part of a LOB

Erasing Part of a LOB

linsert.java

Inserting a row by initializing LOB locator bind variable

Inserting a Row by Initializing a LOB Locator Bind Variable

linstr.java

Seeing if pattern exists in LOB (instr)

Patterns: Checking for Patterns in a LOB Using INSTR

lisopen.java

Seeing if LOB is open

Determining Whether a LOB is Open

listempb.java

Seeing if LOB is temporary

Determining Whether a LOB instance Is Temporary

listempc.java

Seeing if LOB is temporary

Determining Whether a LOB instance Is Temporary

llength.java

Getting the length of a LOB

Length: Determining the Length of a LOB

lloaddat.java

Loading a LOB with BFILE data

Loading a LOB with Data from a BFILE

lread.java

Reading data from LOB

Reading Data from a LOB

lsubstr.java

Reading portion of LOB (substr)

Reading a Portion of a LOB (SUBSTR)

ltrim.java

Trimming LOB data

Trimming LOB Data

lwrite.java

Writing data to a LOB

Writing Data to a LOB

lwriteap.java

Writing to the end of LOB (write append)

Appending to a LOB

Glossary

BFILE

A Large Object datatype that is a binary file residing in the file system, outside of the database data files and tablespace. Note that the BFILE datatype is also referred to as an external LOB in some documentation.

Binary Large Object (BLOB)

A Large Object datatype that has content consisting of binary data and is typically used to hold unstructured data. The BLOB datatype is included in the category Persistent LOBs because it resides in the database.

BLOB

Pronounced "bee-lob." See Binary Large Object.

Character Large Object (CLOB)

The LOB datatype that has content consisting of character data in the database character set. A CLOB can be indexed and searched by the interMedia Text search engine.

CLOB

Pronounced "see-lob." See Character Large Object.

external LOB

A Large Object datatype that is stored outside of the database tablespace. The BFILE datatype is the only external LOB datatype. See also BFILE.

internal persistent LOB

A large object (LOB) that is stored in the database in a BLOB/CLOB/NCLOB column.

introspect

To examine attributes or value of an object.

Large Objects (LOBs)

Large Objects include the following SQL datatypes: BLOB, CLOB, NCLOB, and BFILE. These datatypes are designed for storing data that is large in size. See also BFILE, Binary Large Object, Character Large Object, and National Character Large Object.

LOB

See Large Objects.

LOB attribute

A large object datatype that is a field of an object datatype. For example a CLOB field of an object type.

LOB value

The actual data stored by the Large Object. For example, if a BLOB stores a picture, then the value of the BLOB is the data that makes up the image.

National Character Large Object

The LOB datatype that has content consisting of Unicode character data in the database national character set. An NCLOB can be indexed and searched by the interMedia Text search engine.

NCLOB

Pronounced "en-see-lob." See National Character Large Object.

persistent LOB

A BLOB, CLOB, or NCLOB that is stored in the database. A persistent LOB instance can be selected out of a table and used within the scope of your application. The ACID (atomic, consistent, isolated, durable) properties of the instance are maintained just as for any other column type. Persistent LOBs are sometimes also referred to as internal persistent LOBs or just, internal LOBs.

A persistent LOB can exist as a field of an object datatype as well as an instance in a LOB-type column. For example a CLOB attribute of an instance of type object.

See also temporary LOB and external LOB.

tablespace

A database storage unit that groups related logical structures together.

temporary LOB

A BLOB, CLOB, or NCLOB that is accessible and persists only within, the application scope in which it is declared. A temporary LOB does not exist in database tables.

Index
A  B  C  D  E  F  H  I  J  L  M  N  O  P  R  S  T  U  V  W

A

abstract datatypes and LOBs, 1.8

access statistics for LOBs, 7.3

accessing a LOB

using the LOB APIs, 2.6.3

accessing external LOBs, 15.2 amount, 15.13 amount parameter

used with BFILEs, 15.7

appending

writing to the end of a LOB

internal persistent LOBs, 14.20

array read, 14.11 array write, 14.22 assigning OCILobLocator pointers, 6.4.5

B

BFILE class, See JDBC

BFILE-buffering, See JDBC

BFILENAME function, 2.5.2.2, 15.4, 15.5.1

BFILEs

accessing, 15.2

converting to CLOB or NCLOB, 15.7

creating an object in object cache, 5.5

datatype, 1.7

DBMS_LOB read-only procedures, 6.3.8

DBMS_LOB, offset and amount parameters in bytes, 6.3.2

hard links and symbolic links not allowed, 3.3.1

locators, 2.5

maximum number of open, 3.3.2, 3.3.2, 15.18

maximum size, 5.6

multithreaded server, 2.7.2

multithreaded server mode, 15.6.7

not affected by LOB storage properties, 4.4.1

OCI functions to read/examine values, 6.4.9, 6.5.10

OCI read-only functions, 6.4.11, 6.5.11

opening and closing using JDBC, 6.9.19

operating system files, and, 3.3.1

Oracle Objects for OLE (OO4O)

opening/closing methods, 6.8.7

properties, 6.8.11

read-only methods, 6.8.10

Pro*C/C++ precompiler statements, 6.6.6 Pro*COBOL precompiler embedded SQL statements, 6.7.6 reading with DBMS_LOB, 6.3.6 rules for using, 3.3.1 security, 15.5.1, 15.6 storage devices, 1.4.2 storing any operating system file, 1.7 streaming APIs, 6.9.23 using JDBC to read/examine, 6.9.13 using Pro*C/C++ precompiler to open and close, 6.6.9 bind variables, used with LOB locators in OCI, 6.4.6 binds

See also INSERT statements and UPDATE statements

Blob class, 6.5.1.2 BLOB-buffering, See JDBC BLOBs

class, See JDBC

datatype, 1.7

DBMS_LOB, offset and amount parameters in bytes, 6.3.2

modify using DBMS_LOB, 6.3.5

using JDBC to modify, 6.9.7

using JDBC to read/examine BLOB values, 6.9.8

using oracle.sql.BLOB methods to modify, 6.9.7

buffering

disable

internal persistent LOBs, 14.27

enable

internal persistent LOBs, 14.25

flush

internal persistent LOBs, 14.26

LOB buffering subsystem, 5.1.3.2

C

C++, See Pro*C/C++ precompiler

C, See OCI

CACHE / NOCACHE, 4.4.7

caches

object cache, 5.5

callback, 14.10, 14.20, 15.13 CAST, 10.3 catalog views

v$temporary_lobs, 3.2

character data

varying width, 4.2.2

character set ID, 6.3.3

getting the

internal persistent LOBs, 14.4

See CSID parameter charactersets

multibyte, LONG and LOB datatypes, 13.4.3

CHUNK, 4.4.9, 5.6.1 chunk size, 14.21

and LOB storage properties, 4.4.1

multiple of, to improve performance, 14.10

CLOB class, See JDBC CLOB-buffering, See JDBC CLOBs

columns

varying- width character data, 4.2.2

datatype, 1.7

varying-width columns, 4.2.2

DBMS_LOB, offset and amount parameters in characters, 6.3.2 modify using DBMS_LOB, 6.3.5 opening and closing using JDBC, 6.9.18 reading/examining with JDBC, 6.9.11 using JDBC to modify, 6.9.10 Clone method, See Oracle Objects for OLE (OO4O) closing

all open BFILEs, 15.24

BFILEs with CLOSE, 15.23

BFILEs with FILECLOSE, 15.22

clustered tables, 11.5.1 COBOL, See Pro*COBOL precompiler codepoint semantics, 9.2.2 comparing

all or part of two LOBs

internal persistent LOBs, 14.13

all or parts of two BFILEs, 15.15 conventional path load, 3.1.1 conversion

explicit functions for PL/SQL, 10.3

conversion, implicit from CLOB to character type, 9.2 conversions

character set, 15.7

from binary data to character set, 15.7

implicit, between CLOB and VARCHAR2, 10.2

converting

to CLOB, 10.3

copy semantics, 1.6

internal LOBs, 8.3

copying

all or part of a LOB to another LOB

internal persistent LOBs, 14.16

LOB locator

internal persistent LOBs, 14.17

LOB locator for BFILE, 15.19 CSID parameter

setting OCILobRead and OCILobWrite to OCI_UCS2ID, 6.4.1

D

data interface for persistent LOBs, 13

multibyte charactersets, 13.4.3

data interface for remote LOBs, 13.6 data interface in Java, 13.5 DBMS_LOB

updating LOB with bind variable, 5.3.6

WRITE()

passing hexadecimal string to, 14.21

DBMS_LOB functions on a NULL LOB restriction, 4.1.1.1 DBMS_LOB package

available LOB procedures/functions, 6.2, 6.2

for temporary LOBs, 6.3.7

functions/procedures to modify BLOB, CLOB, and NCLOB, 6.3.5

functions/procedures to read/examine internal and external LOBs, 6.3.6

LOADBLOBFROMFILE, 15.7

LOADCLOBFROMFILE, 15.7

LOADFROMFILE(), 15.7

multithreaded server, 2.7.2

multithreaded server mode, 15.6.7

offset and amount parameter guidelines, 6.3.2

open and close, JDBC replacements for, 6.9.16

opening/closing internal and external LOBs, 6.3.9

provide LOB locator before invoking, 6.3.1

read-only functions/procedures for BFILEs, 6.3.8

to work with LOBs, using, 6.3

WRITE()

guidelines, 14.21

DBMS_LOB.GET_STORAGE_LIMIT, 5.6.3 DBMS_LOB.GETCHUNKSIZE, 5.6.1 DBMS_LOB.GETLENGTH return value, 9.2.4 DBMS_LOB.isTemporary, previous workaround for JDBC, 14.28.1 DBMS_LOB.LOADBLOBFROMFILE, 6.3.2 DBMS_LOB.LOADCLOBFROMFILE, 6.3.2 DBMS_LOB.LOADFROMFILE, 6.3.2 DBMS_LOB.READ, 15.13 directories

catalog views, 15.6.5

guidelines for usage, 15.6.6

ownership and privileges, 15.6.1

DIRECTORY name specification, 15.5.1 DIRECTORY object

catalog views, 15.6.5

getting the alias and filename, 15.20

guidelines for usage, 15.6.6

names on Windows platforms, 15.5.1.1

naming convention, 15.5.1

READ permission on object not individual files, 15.6.2

rules for using, 3.3.1

symbolic links, 3.3.1

symbolic links, and, 3.3.1

DIRECTORY objects, 15.3 direct-path load, 3.1.1 displaying

LOB data for internal persistent LOBs, 14.9

domain indexing on LOB columns, 4.5.1

E

embedded SQL statements, See Pro*C/C++ precompiler and Pro*COBOL precompiler

empty LOBs

creating using JDBC, 6.9.24

JDBC, 6.9.24

EMPTY_BLOB() and EMPTY_CLOB, LOB storage properties for, 4.4.1 EMPTY_CLOB()/BLOB()

to initialize internal LOB, 2.5.2.1

equal

one LOB locator to another

internal persistent LOBs, 14.18

erasing

part of LOB

internal persistent LOBs, 14.24

error message documentation, database, Preface example, LOB access statistics, 7.3.1 examples

repercussions of mixing SQL DML with DBMS_LOB, 5.3.4

updated LOB locators, 5.3.5

updating a LOB with a PL/SQL variable, 5.3.6

existence

check for BFILE, 15.17

extensible indexes, 4.5.3 external callout, 5.1.5 external LOBs (BFILEs)

See BFILEs

external LOBs (BFILEs), See BFILEs

F

FILECLOSEALL(), 15.6.6

flushing

LOB buffer, 5.1.4

flushing buffer, 5.1.1 FOR UPDATE clause

LOB locator, 5.3.1

function-based indexes, 4.5.3 function-based indexes on LOB columns, 4.5.3

H

hard links, rules with BFILEs, 3.3.1

hexadecimal string

passing to DBMS_LOB.WRITE(), 14.21

I

implicit assignment and parameter passing for LOB columns, 13.3.2

implicit conversion of CLOB to character type, 9.2

Improved LOB Usability, Accessing LOBs Using SQL Character Functions, 9.1

indexes

function-based, 4.5.3

rebuilding after LONG-to-LOB migration, 11.5.3

indexes on LOB columns

bitmap index not supported, 4.5.1

B-tree index not supported, 4.5.1

domain indexing, 4.5.1

indexes, restrictions, 11.5.3 index-organized tables, restrictions for LOB columns, 4.8 initializing

during CREATE TABLE or INSERT, 8.4

using EMPTY_CLOB(), EMPTY_BLOB(), 2.5.2.1

initializing a LOB column to a non-null value, 4.1.1.2 inline storage, 4.4.1 inline storage, maximum size, 4.4.1 INSERT statements

binds of greater than 4000 bytes, 13.3.7

inserting

a row by initializing a LOB locator

internal persistent LOBs, 8.5

a row by initializing BFILE locator, 15.25 interfaces for LOBs, see programmatic environments IS NULL return value for LOBs, 9.5.2 IS NULL usage with LOBs, 9.5.2

J

Java, See JDBC

java.sql.Blob, 6.9.1

java.sql.Clob, 6.9.1

JDBC

available LOB methods/properties, 6.2

BFILE class

BFILE streaming APIs, 6.9.23

BFILE-buffering, 6.9.14

BLOB and CLOB classes

calling DBMS_LOB package, 6.9.3

checking if BLOB is temporary, 14.28.1

CLOB streaming APIs, 6.9.22

empty LOBs, 6.9.24

encapsulating locators

methods/properties for BLOB-buffering, 6.9.9

methods/properties for CLOB-buffering, 6.9.12

modifying BLOB values, 6.9.7

modifying CLOB values, 6.9.10

modifyng internal LOBs with Java using objects oracle.sql.BLOB/CLOB, 6.9.1

newStreamLob.java, 6.9.23.1

opening and closing BFILEs, 6.9.19

opening and closing CLOBs, 6.9.18

opening and closing LOBs, 6.9.16

reading internal LOBs and external LOBs (BFILEs) with Java, 6.9.2

reading/examining BLOB values, 6.9.8

reading/examining CLOB values, 6.9.11

reading/examining external LOB (BFILE) values, 6.9.13

referencing LOBs, 6.9.4

streaming APIs for LOBs, 6.9.21

syntax references, 6.9.5

trimming LOBs, 6.9.20

using OracleResultSet to reference LOBs, 6.9.4.1

using OUT parameter from OraclePreparedStatement to reference LOBs, 6.9.4.1

writing to empty LOBs, 6.9.24

JDBC 3.0, 6.9.1 JDBC and Empty LOBs, 6.9.24

L

LBS, See Lob Buffering Subsystem (LBS)

length

an internal persistent LOB, 14.15

getting BFILE, 15.18

LENGTH return value for LOBs, 9.2.4 loading

a LOB with BFILE data, 15.7

LOB with data from a BFILE, 14.5

LOB attributes

defined, 1.8

LOB buffering

BLOB-buffering with JDBC, 6.9.9

buffer-enabled locators, 5.1.6

example, 5.1.3.2

flushing the buffer, 5.1.4

flushing the updated LOB through LBS, 5.1.5

guidelines, 5.1.2

OCI example, 5.1.8

OCI functions, 6.4.13

OCILobFlushBuffer(), 5.1.4

Oracle Objects for OLE (OO4O)

methods for internal LOBs, 6.8.8

physical structure of buffer, 5.1.3.1 Pro*C/C++ precompiler statements, 6.6.8 Pro*COBOL precompiler statements, 6.7.8 usage notes, 5.1.3 LOB Buffering SubSystem (LBS) LOB Buffering Subsystem (LBS)

advantages, 5.1.1

buffer-enabled locators, 5.1.5

buffering example using OCI, 5.1.8

example, 5.1.3.2

flushing

updated LOB, 5.1.5

flushing the buffer, 5.1.4 guidelines, 5.1 saving the state of locator to avoid reselect, 5.1.7 usage, 5.1.3 LOB columns

initializing internal LOB to a value, 4.1.3

initializing to contain locator, 2.5.2

initializing to NULL or Empty, 4.1.1

LOB locator

copy semantics, 1.6

external LOBs (BFILEs), 1.6

internal LOBs, 1.6

out-bind variables in OCI, 6.4.6

reference semantics, 1.6

LOB locators, always stored in row, 4.4.1 LOB reads, 7.3 LOB storage

format of varying width character data, 4.2.2

inline and out-of-line storage properties, 4.4.1

LOB writes, 7.3 LOB writes unaligned, 7.3 LOBs

abstract datatypes, members of, 1.8

attributes and abstract datatypes, 1.8

attributes and object cache, 5.5

buffering

caveats, 5.1.1

pages can be aged out, 5.1.4

buffering subsystem, 5.1 buffering usage notes, 5.1.3 datatypes versus LONG, 1.3 external (BFILEs), 1.4.2 flushing, 5.1.1 in partitioned tables, 4.6 in the object cache, 5.5 interfaces, See programmatic environments interMEDIA, 1.9.3 internal

creating an object in object cache, 5.5

internal LOBs

CACHE / NOCACHE, 4.4.7

CHUNK, 4.4.9

ENABLE | DISABLE STORAGE IN ROW, 4.4.10

initializing, 15.13

introduced, 1.4.1

locators, 2.5

locking before updating, 14.2, 14.16, 14.20, 14.21, 14.23, 14.24

LOGGING / NOLOGGING, 4.4.8

Oracle Objects for OLE (OO4O), modifying methods, 6.8.5

PCTVERSION, 4.4.5, 4.4.5

setting to empty, 4.1.1.2

tablespace and LOB index, 4.4.4

tablespace and storage characteristics, 4.4.2

transactions, 1.4.1

locators, 2.5, 5.3.1 maximum sizes allowed, 5.6 object cache, 5.5 piecewise operations, 5.3.3 read consistent locators, 5.3.1 reason for using, 1.2 setting to contain a locator, 2.5.2 setting to NULL, 4.1.1.1 tables

creating indexes, 4.6.2

moving partitions, 4.6.3

splitting partitions, 4.6.4

unstructured data, 1.2.2 updated LOB locators, 5.3.3 varying-width character data, 4.2.3 LOBs, data interface for remote, 13.6 LOBs, data interface in Java, 13.5 locators, 2.5

BFILEs, 15.6.8

guidelines, 15.6.8.3

two rows can refer to the same file, 15.6.8.1

buffer-enabled, 5.1.6 external LOBs (BFILEs), 2.5 LOB, cannot span transactions, 5.4.4 multiple, 5.3.1 OCI functions, 6.4.12, 6.5.12 Pro*COBOL precompiler statements, 6.7.7 providing in Pro*COBOL precompiler, 6.7.1 read consistent, 5.1.4, 5.1.7, 5.1.7, 5.3.1, 5.3.6, 5.4.4 read consistent locators, 5.3.1 read consistent, updating, 5.3.1 reading and writing to a LOB using, 5.4.1 saving the state to avoid reselect, 5.1.7 see if LOB locator is initialized

internal persistent LOBs, 14.19

selecting within a transaction, 5.4.3 selecting without current transaction, 5.4.2 setting column to contain, 2.5.2 transaction boundaries, 5.4 updated, 5.1.4, 5.3.3, 5.3.6 updating, 5.4.4 LOGGING

migrating LONG-to-LOBs, 11.2.2

LOGGING / NOLOGGING, 4.4.8 LONG versus LOB datatypes, 1.3 LONG-to-LOB Migration, 11.1 LONG-to-LOB migration

ALTER TABLE, 11.4.1

clustered tables, 11.5.1

LOGGING, 11.2.2

NULLs, 11.5.4

rebuilding indexes, 11.5.3

replication, 11.1

triggers, 11.5.2

lONG-to-LOB migration

PL/SQL, 13.3.1

M

migrating

LONG to LOBs, see LONG-to-LOB, 11.1

LONG-to-LOB using ALTER TABLE, 11.4.1

LONG-to-LOBs, constraints maintained, 11.4.1.1

LONG-to-LOBs, indexing, 11.5.3

migration of LONG to LOB in parallel, 11.4.3 multibyte character sets, using with the data interface for LOBs, 13.4.3 multithreaded server

BFILEs, 2.7.2, 15.6.7, 15.6.7

N

national language support

NCLOBs, 1.7

NCLOB parameters allowed as attributes, Preface NCLOBs

datatype, 1.7

DBMS_LOB, offset and amount parameters in characters, 6.3.2

modify using DBMS_LOB, 6.3.5

NewStreamLob.java, 6.9.23.1 NLS_CHARSET_ID, 6.3.3 NOCOPY, using to pass temporary LOB parameters by reference, 7.1.4 ISNULL usage with LOBs, 9.5.2 NULL LOB value, LOB storage for, 4.4.1 NULL LOB values, LOB storage properties for, 4.4.1 NULL LOB, restrictions calling OCI and DBMS_LOB functions, 4.1.1.1

O

object cache, 5.5

creating an object in, 5.5

LOBs, 5.5

OCCI

compared to other interfaces, 6.2

LOB functionality, 6.5

OCCI Bfile class, 6.5.11 OCCI Blob class

read, 6.5.3

write, 6.5.3

OCCI Clob class, 6.5.1

read, 6.5.3

write, 6.5.3

OCI

available LOB functions, 6.2

character set rules, fixed-width and varying-width, 6.4.2

functions for BFILEs, 6.4.11, 6.5.11

functions for temporary LOBs, 6.4.10, 6.5.11

functions to modify internal LOB values, 6.4.8, 6.5.9

functions to open/close internal and external LOBs, 6.4.14, 6.5.13

functions to read or examine internal and external LOB values, 6.4.9, 6.5.10

LOB buffering example, 5.1.8

LOB locator functions, 6.4.12, 6.5.12

Lob-buffering functions, 6.4.13

NCLOB parameters, 6.4.2.2, 6.5.4.1

OCILobFileGetLength

CLOB and NCLOB input and output length, 6.4.2

OCILobRead2()

varying-width CLOB and NCLOB input and amount amounts, 6.4.2

OCILobWrite2()

varying-width CLOB and NCLOB input and amount amounts, 6.4.2, 6.5.3

offset and amount parameter rules

fixed-width character sets, 6.5.2

setting OCILobRead2(), OCILobWrite2() to OCI_UCS2ID, 6.4.1 using to work LOBs, 6.4 OCI functions on a NULL LOB restriction, 4.1.1.1 OCILobArrayRead(), 14.11 OCILobArrayWrite(), 14.22 OCILobAssign(), 5.1.2 OCILobFileSetName(), 15.5, 15.6.8.3 OCILobFlushBuffer(), 5.1.4 OCILobGetChunkSize(), 5.6.1, 5.6.4 OCILobGetStorageLimit(), 5.6.4 OCILobLoadFromFile(), 15.7, 15.7 OCILobLocator in assignment "=" operations, 6.4.5 OCILobLocator, out-bind variables, 6.4.6 OCILobRead2(), 14.9, 14.10, 15.13

BFILEs, 15.13

OCILobWriteAppend2(), 14.20 OCIObjectFlush(), 15.6.8.3 OCIObjectNew(), 15.6.8.3 OCISetAttr(), 15.6.8.3 offset parameter, in DBMS_LOB operations, 6.3.2 OLEDB, 6.10 OO4O, See Oracle Objects for OLE (OO4O) open

checking for open BFILEs with FILEISOPEN(), 15.11

checking if BFILE is open with ISOPEN, 15.10

open, determining whether a LOB is open, 14.8 OpenCloseLob.java example, 6.9.19.4 opening

BFILEs using FILEOPEN, 15.9

BFILEs with OPEN, 15.8

opening and closing LOBs

using JDBC, 6.9.16

ORA-17098

empty LOBs and JDBC, 6.9.24

OraBfile, See Oracle Objects for OLE (OO4O) OraBlob, See Oracle Objects for OLE (OO4O) Oracle Call Interface, See OCI Oracle Objects for OLE (OO4O)

available LOB methods/properties, 6.2

internal LOB buffering, 6.8.8

methods and properties to access data stored in BLOBs, CLOBs, NCLOBs, and BFILEs, 6.8.4

modifying internal LOBs, 6.8.5

opening/closing external LOBs (BFILEs), 6.8.7

OraBfile example

OraBlob example

OraBlob, OraClob, and OraBfile encapsulate locators, 6.8.2

properties for operating on external LOBs (BFILEs), 6.8.11

properties for operating on LOBs, 6.8.9

reading/examining internal LOB and external LOB (BFile) values, 6.8.6

read-only methods for external LOBs (BFILEs), 6.8.10

syntax reference, 6.8.1

using Clone method to retain locator independent of dynaset, 6.8.2.2

OraclePreparedStatement, See JDBC OracleResultSet, See JDBC oracle.sql.BFILE

BFILE-buffering, 6.9.14

JDBC methods to read/examine BFILEs, 6.9.13

oracle.sql.BLOB

for modifying BLOB values, 6.9.7

reading/examining BLOB values, 6.9.8

See JDBC

oracle.sql.BLOBs

BLOB-buffering

oracle.sql.CLOB

CLOB-buffering

JDBC methods to read/examine CLOB values, 6.9.11

modifying CLOB values, 6.9.10

oracle.sql.CLOBs

See JDBC

OraOLEDB, 6.10 out-of-line storage, 4.4.1

P

parallel DML support, 13.3.11

parallel LONG-to-LOB migration, 11.4.3

partitioned index-organized tables

restrictions for LOB columns, 4.8

pattern

check if it exists in BFILE using instr, 15.16

see if it exists IN LOB using (instr)

internal persistent LOBs, 14.14

PCTINCREASE parameter, recommended value for LOBs, 5.7.1 PCTVERSION, 4.4.5, 4.4.5 performance

guidelines

reading/writing large data chunks, 7.1.3

reading/writing large data chunks, temporary LOBs, 7.1.4

PL/SQL, 6.1

and LOBs, semantics changes, 10.1

changing locator-data linkage, 10.3.1

CLOB variables in, 10.3.1

CLOB variables in PL/SQL, 10.3.1

CLOB versus VARCHAR2 comparison, 10.4

CLOBs passed in like VARCHAR2s, 10.3.1

defining a CLOB Variable on a VARCHAR, 10.2

freeing temporary LOBs automatically and manually, 10.3.1

using in LONG-to-LOB migration, 13.3.1

PM schema, 2.5.1 polling, 14.10, 14.20, 15.13 print_media creation, 8.1 print_media table definition, 2.5.1 Pro*C/C++ precompiler

available LOB functions, 6.2, 6.2

LOB buffering, 6.6.8

locators, 6.6.7

modifying internal LOB values, 6.6.3

opening and closing internal LOBs and external LOBs (BFILEs), 6.6.9

providing an allocated input locator pointer, 6.6.1

reading or examining internal and external LOB values, 6.6.4

statements for BFILEs, 6.6.6

statements for temporary LOBs, 6.6.5

Pro*COBOL precompiler

available LOB functions, 6.2

LOB buffering, 6.7.8

locators, 6.7.7

modifying internal LOB values, 6.7.3

providing an allocated input locator, 6.7.1

reading or examining internal and external LOBs, 6.7.4

statements for BFILEs, 6.7.6

temporary LOBs, 6.7.5

programmatic environments

available functions, 6.2

compared, 6.2

programmatic environments for LOBs, 6.1

R

read consistency

LOBs, 5.3.1

read consistent locators, 5.1.4, 5.1.7, 5.1.7, 5.3.1, 5.3.6, 5.4.4 reading

data from a LOB

internal persistent LOBs, 14.10

large data chunks, performance guidelines, 7.1.3 large data chunks, temporary LOBs, 7.1.4 portion of BFILE data using substr, 15.14 portion of LOB using substr

internal persistent LOBs, 14.12

small amounts of data, enable buffering, 14.25 reference semantics, 8.3, 8.3

BFILEs enables multiple BFILE columns for each record, 15.4

replication, 11.1 restrictions

binds of more than 4000 bytes, 13.3.10

cannot call OCI or DBMS_LOB functions on a NULL LOB, 4.1.1.1

clustered tables, 11.5.1

indexes, 11.5.3

index-organized tables and LOBs, 4.8

on LOBs, 2.7

removed, Preface

replication, 11.1

triggers, 11.5.2

retrieving LOB access statistics, 7.3.1 RETURNING clause, using with INSERT to initialize a LOB, 4.1.1.2 round-trips to the server, avoiding, 5.1.1, 5.1.7 rules for using directory objects and BFILEs, 3.3.1

S

sample schema for examples, 8.1

security

BFILEs, 15.5.1, 15.6

BFILEs using SQL DDL, 15.6.3

BFILEs using SQL DML, 15.6.4

SELECT statement

read consistency, 5.3.1

semantics

copy-based for internal LOBs, 8.3

reference based for BFILEs, 15.4

SESSION_MAX_OPEN_FILES parameter, 3.3.2, 3.3.2 setting

internal LOBs to empty, 4.1.1.2

LOBs to NULL, 4.1.1.1

overrides for NLS_LANG variable

SQL

Character Functions, improved, 9.1

features where LOBs cannot be used, 9.4

SQL DDL

BFILE security, 15.6.3

SQL DML

BFILE security, 15.6.4

SQL functions on LOBs

return type, 9.2.3

return value, 9.2.3

temporary LOBs returned, 9.2.3

SQL semantics and LOBs, 9.4 SQL semantics supported for use with LOBs, 9.2 SQL*Loader

conventional path load, 3.1.1

direct-path load, 3.1.1

statistics, access, 7.3 streaming, 14.9

do not enable buffering, when using, 14.25

write, 14.21

streaming APIs

NewStreamLob.java, 6.9.23.1

using JDBC and BFILEs, 6.9.23

using JDBC and CLOBs, 6.9.22

using JDBC and LOBs, 6.9.21

symbolic links, rules with DIRECTORY objects and BFILEs, 3.3.1 system owned object, See DIRECTORY object

T

temporary BLOB

checking if temporary using JDBC, 14.28.1

temporary LOBs

checking if LOB is temporary, 14.28

DBMS_LOB available functions/procedures, 6.3.7

OCI functions, 6.4.10, 6.5.11

Pro*C/C++ precompiler embedded SQL statements, 6.6.5

Pro*COBOL precompiler statements, 6.7.5

returned from SQL functions, 9.2.3

TO_BLOB(),TO_CHAR(), TO_NCHAR(), 10.3 TO_CHAR(), 10.3 TO_CLOB()

converting VARCHAR2,NVARCHAR2,NCLOB to CLOB, 10.3

TO_NCLOB(), 10.3 transaction boundaries

LOB locators, 5.4

transaction IDs, 5.4.1 transactions

external LOBs do not participate in, 1.5

IDs of locators, 5.4

internal LOBs participate in database transactions, 1.4.1

LOB locators cannot span, 5.4.4

locators with non-serializable, 5.4.1

locators with serializable, 5.4.1

migrating from, 5.1.5

triggers

LONG-to-LOB migration, 11.5.2

trimming

LOB data

internal persistent LOBs, 14.23

trimming LOBs using JDBC, 6.9.20

U

UB8MAXVAL is BFILE maximum size, 5.6

UCS2 Unicode character set

varying width character data, 4.2.2

UNICODE

VARCHAR2 and CLOBs support, 9.2.1

unstructured data, 1.2.2 UPDATE statements

binds of greater than 4000 bytes, 13.3.7

updated locators, 5.1.4, 5.3.3, 5.3.6 updating

avoid the LOB with different locators, 5.3.5

LOB values using one locator, 5.3.5

LOB values, read consistent locators, 5.3.1

LOB with PL/SQL bind variable, 5.3.6

LOBs using SQL and DBMS_LOB, 5.3.4

locators, 5.4.4

locking before, 14.16

locking prior to, 14.2, 14.23, 14.24

V

V$NLS_VALID_VALUES, 6.3.3

VARCHAR2

accessing CLOB data when treated as, 10.2

also RAW, applied to CLOBs and BLOBs, 9.5

defining CLOB variable on, 10.2

VARCHAR2, using SQL functions and operators with LOBs, 9.2 VARRAY

LOB restriction, 2.7.1

varying-width character data, 4.2.2 views on DIRECTORY object, 15.6.5 Visual Basic, See Oracle Objects for OLE(OO4O)

W

WHERE Clause Usage with LOBs, 9.5.3

writing

data to a LOB

internal persistent LOBs, 14.21

large data chunks, performance guidelines, 7.1.3 large data chunks, temporary LOBs, 7.1.4 singly or piecewise, 14.20 small amounts of data, enable buffering, 14.25

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