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Oracle Data Guard Concepts and Administration
Release 2 (9.2)

Part Number A96653-02
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A standby database is the most effective disaster recovery solution for an Oracle database because a standby database can be used to run your production system if your primary database becomes unusable. A standby database can also be used to remedy problems caused by user errors, data corruption, and other operational difficulties.

This guide describes Oracle Data Guard concepts, and helps you configure and implement standby databases.

This preface contains the following topics:


Oracle Data Guard Concepts and Administration is intended for database administrators (DBAs) who administer the backup, restoration, and recovery operations of an Oracle database system.

To use this document, you should be familiar with relational database concepts and basic backup and recovery administration. You should also be familiar with the operating system environment under which you are running Oracle.

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. Standards will continue to evolve over time, and Oracle Corporation 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 additional information, visit the Oracle Accessibility Program Web site at

Accessibility of Code Examples in Documentation

JAWS, a Windows screen reader, 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, JAWS may not always read a line of text that consists solely of a bracket or brace.


This document contains:

Part I, "Concepts and Administration"

Chapter 1, "Introduction to Oracle Data Guard"

This chapter offers a general overview of the Oracle9i Data Guard architecture.

Chapter 2, "Getting Started with Data Guard"

This chapter introduces physical, logical, and cascading standby databases.

Chapter 3, "Creating a Physical Standby Database"

This chapter explains how to create a physical standby database and start applying redo logs to it.

Chapter 4, "Creating a Logical Standby Database"

This chapter explains how to create a logical standby database and start applying redo logs to it.

Chapter 5, "Log Transport Services"

This chapter introduces log transport services. It describes the data protection modes that protect the production database against loss in the event of an unplanned outage and it provides procedures and guidelines for configuring log transport services on a primary and standby database.

Chapter 6, "Log Apply Services"

This chapter introduces log apply services. It provides guidelines for managing log apply services for physical and logical standby databases.

Chapter 7, "Role Management"

This chapter introduces role management services. It provides information about database failover and switchover role transitions.

Chapter 8, "Managing a Physical Standby Database"

This chapter describes how to manage a physical standby database. It provides information on monitoring and responding to events that affect the database role.

Chapter 9, "Managing a Logical Standby Database"

This chapter describes how to manage a logical standby database. It provides information on applying redo logs, system tuning, and tablespace management.

Chapter 10, "Data Guard Scenarios"

This chapter describes common database scenarios such as creating, recovering, failing over, switching over, configuring, and backing up standby and primary databases.

Part II, "Reference"

Chapter 11, "Initialization Parameters"

This reference chapter describes initialization parameters for each Oracle instance, including the primary database and each standby database in the Data Guard environment.

Chapter 12, "LOG_ARCHIVE_DEST_n Parameter Attributes"

This reference chapter provides syntax and examples for the attributes of the LOG_ARCHIVE_DEST_n initialization parameter.

Chapter 13, "SQL Statements"

This reference chapter provides SQL statements that are useful for performing operations on a standby database.

Chapter 14, "Views"

This reference chapter lists views that contain useful information for monitoring the Data Guard environment. It summarizes the columns contained in each view and provides a description for each column.

Part III, "Appendixes and Glossary"

Appendix A, "Troubleshooting the Standby Database"

This appendix discusses troubleshooting for the standby database.

Appendix B, "Manual Recovery"

This appendix describes managing a physical standby database in manual recovery mode. It provides instructions for manually resolving archive gaps and renaming standby files not captured by conversion parameters.

Appendix C, "Standby Database Real Application Clusters Support"

This appendix describes the primary and standby database configurations in a Real Application Clusters environment.

Appendix D, "Cascaded Redo Log Destinations"

This appendix describes how to implement cascaded redo log destinations, whereby a standby database receives its redo logs from another standby database, instead of directly from the primary database.

Appendix E, "Sample Disaster Recovery ReadMe File"

This appendix provides a sample ReadMe file that includes the kind of information that the person who is making disaster recovery decisions would need when deciding which standby database should be the target of the failover operation.


Related Documentation

Every reader of Oracle Data Guard Concepts and Administration should have read:

You will often need to refer to the following guides:

If you need to migrate existing standby databases to this Oracle9i release, see Oracle9i Database Migration for complete instructions. In addition, refer to Oracle9i Database Concepts for information about other Oracle products and features that provide disaster recovery and high data availability solutions.

In North America, printed documentation is available for sale in the Oracle Store at

Customers in Europe, the Middle East, and Africa (EMEA) can purchase documentation from

Other customers can contact their Oracle representative to purchase printed documentation.

To download free release notes, installation documentation, white papers, or other collateral, please visit the Oracle Technology Network (OTN). You must register online before using OTN; registration is free and can be done at

If you already have a username and password for OTN, then you can go directly to the documentation section of the OTN Web site at

To access the database documentation search engine directly, please visit


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

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 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.


Italic typeface indicates book titles or emphasis.

Oracle9i 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.


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, network 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 /disk/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 Code Examples

Code 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 code 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.



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.




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.

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;


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

CONNECT SYSTEM/system_password

DB_NAME = database_name


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;


DROP TABLE hr.employees;


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