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Oracle® Database Advanced Application Developer's Guide
11g Release 2 (11.2)

Part Number E17125-03
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12 Using Oracle Flashback Technology

This chapter explains how to use Oracle Flashback Technology in database applications.

Topics:

Overview of Oracle Flashback Technology

Oracle Flashback Technology is a group of Oracle Database features that let you view past states of database objects or to return database objects to a previous state without using point-in-time media recovery.

With flashback features, you can:

Oracle Flashback features use the Automatic Undo Management (AUM) system to obtain metadata and historical data for transactions. They rely on undo data, which are records of the effects of individual transactions. For example, if a user runs an UPDATE statement to change a salary from 1000 to 1100, then Oracle Database stores the value 1000 in the undo data.

Undo data is persistent and survives a database shutdown. By using flashback features, you can use undo data to query past data or recover from logical damage. Besides using it in flashback features, Oracle Database uses undo data to perform these actions:

Topics:

For additional general information about flashback features, see Oracle Database Concepts

Application Development Features

In application development, you can use these flashback features to report historical data or undo erroneous changes. (You can also use these features interactively as a database user or administrator.)

Oracle Flashback Query

Use this feature to retrieve data for an earlier time that you specify with the AS OF clause of the SELECT statement. For more information, see "Using Oracle Flashback Query (SELECT AS OF)".

Oracle Flashback Version Query

Use this feature to retrieve metadata and historical data for a specific time interval (for example, to view all the rows of a table that ever existed during a given time interval). Metadata for each row version includes start and end time, type of change operation, and identity of the transaction that created the row version. To create an Oracle Flashback Version Query, use the VERSIONS BETWEEN clause of the SELECT statement. For more information, see "Using Oracle Flashback Version Query".

Oracle Flashback Transaction Query

Use this feature to retrieve metadata and historical data for a given transaction or for all transactions in a given time interval. To perform an Oracle Flashback Transaction Query, select from the static data dictionary view FLASHBACK_TRANSACTION_QUERY. For more information, see "Using Oracle Flashback Transaction Query".

Typically, you use Oracle Flashback Transaction Query with an Oracle Flashback Version Query that provides the transaction IDs for the rows of interest (see "Using Oracle Flashback Transaction Query with Oracle Flashback Version Query").

DBMS_FLASHBACK Package

Use this feature to set the internal Oracle Database clock to an earlier time so that you can examine data that was current at that time, or to roll back a transaction and its dependent transactions while the database remains online (see Flashback Transaction). For more information, see "Using DBMS_FLASHBACK Package".

Flashback Transaction

Use Flashback Transaction to roll back a transaction and its dependent transactions while the database remains online. This recovery operation uses undo data to create and run the corresponding compensating transactions that return the affected data to its original state. (Flashback Transaction is part of DBMS_FLASHBACK package.) For more information, see "Using DBMS_FLASHBACK Package".

Flashback Data Archive (Oracle Total Recall)

Use Flashback Data Archive to automatically track and archive both regular queries and Oracle Flashback Query, ensuring SQL-level access to the versions of database objects without getting a snapshot-too-old error. For more information, see "Using Flashback Data Archive (Oracle Total Recall)".

Database Administration Features

These flashback features are primarily for data recovery. Typically, you use these features only as a database administrator.

This chapter focuses on the "Application Development Features". For more information about the database administration features, see Oracle Database Administrator's Guide and the Oracle Database Backup and Recovery User's Guide.

Oracle Flashback Table

Use this feature to restore a table to its state at a previous point in time. You can restore a table while the database is on line, undoing changes to only the specified table.

Oracle Flashback Drop

Use this feature to recover a dropped table. This feature reverses the effects of a DROP TABLE statement.

Oracle Flashback Database

Use this feature to quickly return the database to an earlier point in time, by undoing all of the changes that have taken place since then. This is fast, because you do not have to restore database backups.

Configuring Your Database for Oracle Flashback Technology

Before you can use flashback features in your application, you or your database administrator must perform the configuration tasks described in these topics:

Configuring Your Database for Automatic Undo Management

To configure your database for Automatic Undo Management (AUM), you or your database administrator must:

  • Create an undo tablespace with enough space to keep the required data for flashback operations.

    The more often users update the data, the more space is required. The database administrator usually calculates the space requirement.

  • Enable AUM, as explained in Oracle Database Administrator's Guide. Set these database initialization parameters:

    • UNDO_MANAGEMENT

    • UNDO_TABLESPACE

    • UNDO_RETENTION

    For a fixed-size undo tablespace, Oracle Database automatically tunes the system to give the undo tablespace the best possible undo retention.

    For an automatically extensible undo tablespace, Oracle Database retains undo data longer than the longest query duration and the low threshold of undo retention specified by the UNDO_RETENTION parameter.

    Note:

    You can query V$UNDOSTAT.TUNED_UNDORETENTION to determine the amount of time for which undo is retained for the current undo tablespace. For more information about V$UNDOSTAT, see Oracle Database Reference.

    Setting UNDO_RETENTION does not guarantee that unexpired undo data is not discarded. If the system needs more space, Oracle Database can overwrite unexpired undo with more recently generated undo data.

  • Specify the RETENTION GUARANTEE clause for the undo tablespace to ensure that unexpired undo data is not discarded.

See Also:

Oracle Database Administrator's Guide for more information about creating an undo tablespace and enabling AUM

Configuring Your Database for Oracle Flashback Transaction Query

To configure your database for the Oracle Flashback Transaction Query feature, you or your database administrator must:

  • Ensure that Oracle Database is running with version 10.0 compatibility.

  • Enable supplemental logging:

    ALTER DATABASE ADD SUPPLEMENTAL LOG DATA;
    

Configuring Your Database for Flashback Transaction

To configure your database for the Flashback Transaction feature, you or your database administrator must:

  • With the database mounted but not open, enable ARCHIVELOG:

    ALTER DATABASE ARCHIVELOG;
    
  • Open at least one archive log:

    ALTER SYSTEM ARCHIVE LOG CURRENT;
    
  • If not done, enable minimal and primary key supplemental logging:

    ALTER DATABASE ADD SUPPLEMENTAL LOG DATA;
    ALTER DATABASE ADD SUPPLEMENTAL LOG DATA (PRIMARY KEY) COLUMNS;
    
  • If you want to track foreign key dependencies, enable foreign key supplemental logging:

    ALTER DATABASE ADD SUPPLEMENTAL LOG DATA (FOREIGN KEY) COLUMNS;
    

Note:

If you have very many foreign key constraints, enabling foreign key supplemental logging might not be worth the performance penalty.

Enabling Oracle Flashback Operations on Specific LOB Columns

To enable flashback operations on specific LOB columns of a table, use the ALTER TABLE statement with the RETENTION option.

Because undo data for LOB columns can be voluminous, you must define which LOB columns to use with flashback operations.

See Also:

Oracle Database SecureFiles and Large Objects Developer's Guide to learn about LOB storage and the RETENTION parameter

Granting Necessary Privileges

You or your database administrator must grant privileges to users, roles, or applications that must use these flashback features. For information about the GRANT statement, see Oracle Database SQL Language Reference.

For Oracle Flashback Query and Oracle Flashback Version Query

To allow access to specific objects during queries, grant FLASHBACK and SELECT privileges on those objects.

To allow queries on all tables, grant the FLASHBACK ANY TABLE privilege.

For Oracle Flashback Transaction Query

Grant the SELECT ANY TRANSACTION privilege.

To allow execution of undo SQL code retrieved by an Oracle Flashback Transaction Query, grant SELECT, UPDATE, DELETE, and INSERT privileges for specific tables.

For DBMS_FLASHBACK Package

To allow access to the features in the DBMS_FLASHBACK package, grant the EXECUTE privilege on DBMS_FLASHBACK.

For Flashback Data Archive (Oracle Total Recall)

To allow a specific user to enable Flashback Data Archive on tables, using a specific Flashback Data Archive, grant the FLASHBACK ARCHIVE object privilege on that Flashback Data Archive to that user. To grant the FLASHBACK ARCHIVE object privilege, you must either be logged on as SYSDBA or have FLASHBACK ARCHIVE ADMINISTER system privilege.

To allow execution of these statements, grant the FLASHBACK ARCHIVE ADMINISTER system privilege:

  • CREATE FLASHBACK ARCHIVE

  • ALTER FLASHBACK ARCHIVE

  • DROP FLASHBACK ARCHIVE

To grant the FLASHBACK ARCHIVE ADMINISTER system privilege, you must be logged on as SYSDBA.

To create a default Flashback Data Archive, using either the CREATE FLASHBACK ARCHIVE or ALTER FLASHBACK ARCHIVE statement, you must be logged on as SYSDBA.

To disable Flashback Data Archive for a table that has been enabled for Flashback Data Archive, you must either be logged on as SYSDBA or have the FLASHBACK ARCHIVE ADMINISTER system privilege.

Using Oracle Flashback Query (SELECT AS OF)

To use Oracle Flashback Query, use a SELECT statement with an AS OF clause. Oracle Flashback Query retrieves data as it existed at an earlier time. The query explicitly references a past time through a time stamp or System Change Number (SCN). It returns committed data that was current at that point in time.

Uses of Oracle Flashback Query include:

Topics:

For more information about the SELECT AS OF statement, see Oracle Database SQL Language Reference.

Example of Examining and Restoring Past Data

Suppose that you discover at 12:30 PM that the row for employee Chung was deleted from the employees table, and you know that at 9:30AM the data for Chung was correctly stored in the database. You can use Oracle Flashback Query to examine the contents of the table at 9:30 AM to find out what data was lost. If appropriate, you can restore the lost data.

Example 12-1 retrieves the state of the record for Chung at 9:30AM, April 4, 2004:

Example 12-1 Retrieving a Lost Row with Oracle Flashback Query

SELECT * FROM employees
AS OF TIMESTAMP
TO_TIMESTAMP('2004-04-04 09:30:00', 'YYYY-MM-DD HH:MI:SS')
WHERE last_name = 'Chung';

Example 12-2 restores Chung's information to the employees table:

Example 12-2 Restoring a Lost Row After Oracle Flashback Query

INSERT INTO employees (
  SELECT * FROM employees
  AS OF TIMESTAMP
  TO_TIMESTAMP('2004-04-04 09:30:00', 'YYYY-MM-DD HH:MI:SS')
  WHERE last_name = 'Chung'
);

Guidelines for Oracle Flashback Query

  • You can specify or omit the AS OF clause for each table and specify different times for different tables.

    Note:

    If a table is a Flashback Data Archive and you specify a time for it that is earlier than its creation time, the query returns zero rows for that table, rather than causing an error. (For information about Flashback Data Archives, see "Using Flashback Data Archive (Oracle Total Recall)".)
  • You can use the AS OF clause in queries to perform data definition language (DDL) operations (such as creating and truncating tables) or data manipulation language (DML) statements (such as INSERT and DELETE) in the same session as Oracle Flashback Query.

  • To use the result of Oracle Flashback Query in a DDL or DML statement that affects the current state of the database, use an AS OF clause inside an INSERT or CREATE TABLE AS SELECT statement.

  • If a possible 3-second error (maximum) is important to Oracle Flashback Query in your application, use an SCN instead of a time stamp. See "General Guidelines for Oracle Flashback Technology".

  • You can create a view that refers to past data by using the AS OF clause in the SELECT statement that defines the view.

    If you specify a relative time by subtracting from the current time on the database host, the past time is recalculated for each query. For example:

    CREATE VIEW hour_ago AS
      SELECT * FROM employees
        AS OF TIMESTAMP (SYSTIMESTAMP - INTERVAL '60' MINUTE);
    

    SYSTIMESTAMP refers to the time zone of the database host environment.

  • You can use the AS OF clause in self-joins, or in set operations such as INTERSECT and MINUS, to extract or compare data from two different times.

    You can store the results by preceding Oracle Flashback Query with a CREATE TABLE AS SELECT or INSERT INTO TABLE SELECT statement. For example, this query reinserts into table employees the rows that existed an hour ago:

    INSERT INTO employees
        (SELECT * FROM employees
         AS OF TIMESTAMP (SYSTIMESTAMP - INTERVAL '60' MINUTE)
        )
        MINUS SELECT * FROM employees);
    

    SYSTIMESTAMP refers to the time zone of the database host environment.

Using Oracle Flashback Version Query

Use Oracle Flashback Version Query to retrieve the different versions of specific rows that existed during a given time interval. A row version is created whenever a COMMIT statement is executed.

Specify Oracle Flashback Version Query using the VERSIONS BETWEEN clause of the SELECT statement. The syntax is:

VERSIONS {BETWEEN {SCN | TIMESTAMP} start AND end}

where start and end are expressions representing the start and end, respectively, of the time interval to be queried. The time interval includes (start and end).

Oracle Flashback Version Query returns a table with a row for each version of the row that existed at any time during the specified time interval. Each row in the table includes pseudocolumns of metadata about the row version, described in Table 12-1. This information can reveal when and how a particular change (perhaps erroneous) occurred to your database.

Table 12-1 Oracle Flashback Version Query Row Data Pseudocolumns

Pseudocolumn Name Description

VERSIONS_STARTSCN

VERSIONS_STARTTIME

Starting System Change Number (SCN) or TIMESTAMP when the row version was created. This pseudocolumn identifies the time when the data first had the values reflected in the row version. Use this pseudocolumn to identify the past target time for Oracle Flashback Table or Oracle Flashback Query.

If this pseudocolumn is NULL, then the row version was created before start.

VERSIONS_ENDSCN

VERSIONS_ENDTIME

SCN or TIMESTAMP when the row version expired.

If this pseudocolumn is NULL, then either the row version was current at the time of the query or the row corresponds to a DELETE operation.

VERSIONS_XID

Identifier of the transaction that created the row version.

VERSIONS_OPERATION

Operation performed by the transaction: I for insertion, D for deletion, or U for update. The version is that of the row that was inserted, deleted, or updated; that is, the row after an INSERT operation, the row before a DELETE operation, or the row affected by an UPDATE operation.

For user updates of an index key, Oracle Flashback Version Query might treat an UPDATE operation as two operations, DELETE plus INSERT, represented as two version rows with a D followed by an I VERSIONS_OPERATION.


A given row version is valid starting at its time VERSIONS_START* up to, but not including, its time VERSIONS_END*. That is, it is valid for any time t such that VERSIONS_START* <= t < VERSIONS_END*. For example, this output indicates that the salary was 10243 from September 9, 2002, included, to November 25, 2003, excluded.

VERSIONS_START_TIME     VERSIONS_END_TIME     SALARY
-------------------     -----------------     ------
09-SEP-2003             25-NOV-2003           10243

Here is a typical use of Oracle Flashback Version Query:

SELECT versions_startscn, versions_starttime,
       versions_endscn, versions_endtime,
       versions_xid, versions_operation,
       last_name, salary
  FROM employees
  VERSIONS BETWEEN TIMESTAMP
      TO_TIMESTAMP('2008-12-18 14:00:00', 'YYYY-MM-DD HH24:MI:SS')
  AND TO_TIMESTAMP('2008-12-18 17:00:00', 'YYYY-MM-DD HH24:MI:SS')
  WHERE first_name = 'John';

You can use VERSIONS_XID with Oracle Flashback Transaction Query to locate this transaction's metadata, including the SQL required to undo the row change and the user responsible for the change—see "Using Oracle Flashback Transaction Query".

See Also:

Oracle Database SQL Language Reference for information about Oracle Flashback Version Query pseudocolumns and the syntax of the VERSIONS clause

Using Oracle Flashback Transaction Query

Use Oracle Flashback Transaction Query to retrieve metadata and historical data for a given transaction or for all transactions in a given time interval. Oracle Flashback Transaction Query queries the static data dictionary view FLASHBACK_TRANSACTION_QUERY, whose columns are described in Oracle Database Reference.

The column UNDO_SQL shows the SQL code that is the is the logical opposite of the DML operation performed by the transaction. You can usually use this code to reverse the logical steps taken during the transaction. However, there are cases where the SQL_UNDO code is not the exact opposite of the original transaction. For example, a SQL_UNDO INSERT operation might not insert a row back in a table at the same ROWID from which it was deleted.

This statement queries the FLASHBACK_TRANSACTION_QUERY view for transaction information, including the transaction ID, the operation, the operation start and end SCNs, the user responsible for the operation, and the SQL code that shows the logical opposite of the operation:

SELECT xid, operation, start_scn, commit_scn, logon_user, undo_sql
FROM flashback_transaction_query
WHERE xid = HEXTORAW('000200030000002D');

This statement uses Oracle Flashback Version Query as a subquery to associate each row version with the LOGON_USER responsible for the row data change:

SELECT xid, logon_user
FROM flashback_transaction_query
WHERE xid IN (
  SELECT versions_xid FROM employees VERSIONS BETWEEN TIMESTAMP
  TO_TIMESTAMP('2003-07-18 14:00:00', 'YYYY-MM-DD HH24:MI:SS') AND
  TO_TIMESTAMP('2003-07-18 17:00:00', 'YYYY-MM-DD HH24:MI:SS')
);

Note:

If you query FLASHBACK_TRANSACTION_QUERY without specifying XID in the WHERE clause, the query scans many unrelated rows, degrading performance.

See Also:

Using Oracle Flashback Transaction Query with Oracle Flashback Version Query

In this example, a database administrator does this:

DROP TABLE emp;
CREATE TABLE emp (
  empno   NUMBER PRIMARY KEY,
  empname VARCHAR2(16),
  salary  NUMBER
);
INSERT INTO emp (empno, empname, salary) VALUES (111, 'Mike', 555);
COMMIT;

DROP TABLE dept;
CREATE TABLE dept (
  deptno   NUMBER,
  deptname VARCHAR2(32)
);
INSERT INTO dept (deptno, deptname) VALUES (10, 'Accounting');
COMMIT;

Now emp and dept have one row each. In terms of row versions, each table has one version of one row. Suppose that an erroneous transaction deletes empno 111 from table emp:

UPDATE emp SET salary = salary + 100 WHERE empno = 111;
INSERT INTO dept (deptno, deptname) VALUES (20, 'Finance');
DELETE FROM emp WHERE empno = 111;
COMMIT;

Next, a transaction reinserts empno 111 into the emp table with a new employee name:

INSERT INTO emp (empno, empname, salary) VALUES (111, 'Tom', 777);
UPDATE emp SET salary = salary + 100 WHERE empno = 111;
UPDATE emp SET salary = salary + 50 WHERE empno = 111;
COMMIT;

The database administrator detects the application error and must diagnose the problem. The database administrator issues this query to retrieve versions of the rows in the emp table that correspond to empno 111. The query uses Oracle Flashback Version Query pseudocolumns:

SELECT versions_xid XID, versions_startscn START_SCN,
  versions_endscn END_SCN, versions_operation OPERATION,
  empname, salary
FROM emp
VERSIONS BETWEEN SCN MINVALUE AND MAXVALUE
WHERE empno = 111;

Results are similar to:

XID               START_SCN    END_SCN O EMPNAME              SALARY
---------------- ---------- ---------- - ---------------- ----------
09001100B2200000   10093466            I Tom                     927
030002002B210000   10093459            D Mike                    555
0800120096200000   10093375   10093459 I Mike                    555
 
3 rows selected.

The results table rows are in descending chronological order. The third row corresponds to the version of the row in the table emp that was inserted in the table when the table was created. The second row corresponds to the row in emp that the erroneous transaction deleted. The first row corresponds to the version of the row in emp that was reinserted with a new employee name.

The database administrator identifies transaction 030002002B210000 as the erroneous transaction and uses Oracle Flashback Transaction Query to audit all changes made by this transaction:

SELECT  xid, start_scn, commit_scn, operation, logon_user, undo_sql
FROM flashback_transaction_query
WHERE xid = HEXTORAW('000200030000002D');

Results are similar to:

XID               START_SCN COMMIT_SCN OPERATION LOGON_USER
---------------- ---------- ---------- --------- ------------------------------
UNDO_SQL
--------------------------------------------------------------------------------
 
030002002B210000   10093452   10093459 DELETE    HR
insert into "HR"."EMP"("EMPNO","EMPNAME","SALARY") values ('111','Mike','655');
 
030002002B210000   10093452   10093459 INSERT    HR
delete from "HR"."DEPT" where ROWID = 'AAATjuAAEAAAAJrAAB';
 
030002002B210000   10093452   10093459 UPDATE    HR
update "HR"."EMP" set "SALARY" = '555' where ROWID = 'AAATjsAAEAAAAJ7AAA';
 
030002002B210000   10093452   10093459 BEGIN     HR
 
 
4 rows selected.

To make the result of the next query easier to read, the database administrator uses these SQL*Plus commands:

COLUMN operation FORMAT A9
COLUMN table_name FORMAT A10
COLUMN table_owner FORMAT A11

To see the details of the erroneous transaction and all subsequent transactions, the database administrator performs this query:

SELECT xid, start_scn, commit_scn, operation, table_name, table_owner
FROM flashback_transaction_query
WHERE table_owner = 'HR'
AND start_timestamp >=
  TO_TIMESTAMP ('2002-04-16 11:00:00','YYYY-MM-DD HH:MI:SS');

Results are similar to:

XID               START_SCN COMMIT_SCN OPERATION TABLE_NAME TABLE_OWNER
---------------- ---------- ---------- --------- ---------- -----------
02000E0074200000   10093435   10093446 INSERT    DEPT       HR
030002002B210000   10093452   10093459 DELETE    EMP        HR
030002002B210000   10093452   10093459 INSERT    DEPT       HR
030002002B210000   10093452   10093459 UPDATE    EMP        HR
0800120096200000   10093374   10093375 INSERT    EMP        HR
09001100B2200000   10093462   10093466 UPDATE    EMP        HR
09001100B2200000   10093462   10093466 UPDATE    EMP        HR
09001100B2200000   10093462   10093466 INSERT    EMP        HR
 
8 rows selected.

Note:

Because the preceding query does not specify the XID in the WHERE clause, it scans many unrelated rows, degrading performance.

Using ORA_ROWSCN

ORA_ROWSCN is a pseudocolumn of any table that is not fixed or external. It represents the SCN of the most recent change to a given row in the current session; that is, the most recent COMMIT operation for the row in the current session. For example:

SELECT ora_rowscn, last_name, salary
FROM employees
WHERE employee_id = 200;

Result is similar to:

ORA_ROWSCN LAST_NAME                     SALARY
---------- ------------------------- ----------
    884320 Whalen                          2800

The most recent COMMIT operation for the row in the current session took place at approximately SCN 9371092. To convert an SCN to the corresponding TIMESTAMP value, use the function SCN_TO_TIMESTAMP (documented in Oracle Database SQL Language Reference).

ORA_ROWSCN is a conservative upper bound of the latest commit time—the actual commit SCN can be somewhat earlier. ORA_ROWSCN is more precise (closer to the actual commit SCN) for a row-dependent table (created using CREATE TABLE with the ROWDEPENDENCIES clause). For more information about ORA_ROWSCN and ROWDEPENDENCIES, see Oracle Database SQL Language Reference.

Note:

ORA_ROWSCN is not supported for Flashback Query. Instead, use the version query pseudocolumns, which are provided explicitly for Flashback Query. For information about these pseudocolumns, see Oracle Database SQL Language Reference.

Topics:

Scenario: Package Subprogram Might Change Row

Your application examines a row of data and records the corresponding ORA_ROWSCN as 202553. Then, your application invokes a package subprogram, whose implementation details you cannot see, which might or might not change the same row (and commit the change). Later, your application must update the row only if the package subprogram did not change it. Make the operation conditional—update the row only if ORA_ROWSCN is still 202553, as in this equivalent interactive statement:

UPDATE employees
SET salary = salary + 100
WHERE employee_id = 200
AND ora_rowscn = 202553;

If the package subprogram changed the row, then ORA_ROWSCN is no longer 9371092, and the update fails.

Your application queries again to obtain the new row data and ORA_ROWSCN. Suppose that the ORA_ROWSCN is now 415639. The application tries the conditional update again, using the new ORA_ROWSCN. This time, the update succeeds, and it is committed. An interactive equivalent is:

UPDATE employees
SET salary = salary + 100
WHERE employee_id = 7788
AND ora_rowscn = 415639;

ORA_ROWSCN and Tables with Virtual Private Database (VPD)

When a VPD policy is added to a table, it is no longer possible to select the ORA_ROWSCN pseudocolumn. However, because ORA_ROWSCN is available inside the policy function, you can:

  1. Create a function that returns a row SCN, as in Example 12-3.

  2. In the policy predicate function, add a predicate that stores the row SCN in the context that the function uses while processing rows. For example:

    ||' AND f_ora_rowscn('||object_name||'.ora_rowscn) = 1'
    
  3. Use the function to fetch the row. For example:

    SELECT t.*, get_rowscn(t.rowid) "ORA_ROWSCN" FROM test_table t;
    

Note:

To run Example 12-3, you need CREATE ANY CONTEXT system privilege.

Example 12-3 Function that Can Return Row SCN from Table that has VPD

-- Create context that function uses while processing rows:
 
CREATE OR REPLACE FUNCTION f_ora_rowscn
 (rowscn IN NUMBER)
 RETURN NUMBER
AS
BEGIN
  DBMS_SESSION.SET_CONTEXT('STORE_ROWSCN','ROWSCN',rowscn);
  RETURN 1;
END;
/
 
CREATE CONTEXT store_rowscn USING f_ora_rowscn;
 
-- Create function that returns row SCN for each row:
 
CREATE OR REPLACE FUNCTION get_rowscn
  (r IN ROWID)
  RETURN VARCHAR2
AS
BEGIN 
  RETURN sys_context('STORE_ROWSCN','ROWSCN');
END;
/

Using DBMS_FLASHBACK Package

The DBMS_FLASHBACK package provides the same functionality as Oracle Flashback Query, but Oracle Flashback Query is sometimes more convenient.

The DBMS_FLASHBACK package acts as a time machine: you can turn back the clock, perform normal queries as if you were at that earlier time, and then return to the present. Because you can use the DBMS_FLASHBACK package to perform queries on past data without special clauses such as AS OF or VERSIONS BETWEEN, you can reuse existing PL/SQL code to query the database at earlier times.

You must have the EXECUTE privilege on the DBMS_FLASHBACK package.

To use the DBMS_FLASHBACK package in your PL/SQL code:

  1. Specify a past time by invoking either DBMS_FLASHBACK.ENABLE_AT_TIME or DBMS_FLASHBACK.ENABLE_AT_SYSTEM_CHANGE_NUMBER.

  2. Perform regular queries (that is, queries without special flashback-feature syntax such as AS OF). Do not perform DDL or DML operations.

    The database is queried at the specified past time.

  3. Return to the present by invoking DBMS_FLASHBACK.DISABLE.

    You must invoke DBMS_FLASHBACK.DISABLE before invoking DBMS_FLASHBACK.ENABLE_AT_TIME or DBMS_FLASHBACK.ENABLE_AT_SYSTEM_CHANGE_NUMBER again. You cannot nest enable/disable pairs.

To use a cursor to store the results of queries, open the cursor before invoking DBMS_FLASHBACK.DISABLE. After storing the results and invoking DBMS_FLASHBACK.DISABLE, you can:

You can invoke DBMS_FLASHBACK.GET_SYSTEM_CHANGE_NUMBER at any time to get the current System Change Number (SCN). DBMS_FLASHBACK.GET_SYSTEM_CHANGE_NUMBER always returns the current SCN regardless of previous invocations of DBMS_FLASHBACK.ENABLE.

See Also:

Using Flashback Transaction

The DBMS_FLASHBACK.TRANSACTION_BACKOUT procedure rolls back a transaction and its dependent transactions while the database remains online. This recovery operation uses undo data to create and run the compensating transactions that return the affected data to its original state.

The transactions being rolled back are subject to these restrictions:

See Also:

Topics:

Dependent Transactions

In the context of Flashback Transaction, transaction 2 can depend on transaction 1 in any of these ways:

  • Write-after-write dependency

    Transaction 1 changes a row of a table, and later transaction 2 changes the same row.

  • Primary key dependency

    A table has a primary key constraint on column c. In a row of the table, column c has the value v. Transaction 1 deletes that row, and later transaction 2 inserts a row into the same table, assigning the value v to column c.

  • Foreign key dependency

    In table b, column b1 has a foreign key constraint on column a1 of table a. Transaction 1 changes a value in a1, and later transaction 2 changes a value in b1.

TRANSACTION_BACKOUT Parameters

The parameters of the TRANSACTION_BACKOUT procedure are:

  • Number of transactions to be backed out

  • List of transactions to be backed out, identified either by name or by XID

  • Time hint, if you identify transactions by name

    Specify a time that is earlier than any transaction started.

  • Backout option from Table 12-2

For the syntax of the TRANSACTION_BACKOUT procedure and detailed parameter descriptions, see Oracle Database PL/SQL Packages and Types Reference.

Table 12-2 Flashback TRANSACTION_BACKOUT Options

Option Description

CASCADE

Backs out specified transactions and all dependent transactions in a post-order fashion (that is, children are backed out before parents are backed out).

Without CASCADE, if any dependent transaction is not specified, an error occurs.

NOCASCADE

Default. Backs out specified transactions, which are expected to have no dependent transactions. First dependent transactions causes an error and appears in *_FLASHBACK_TRANSACTION_REPORT.

NOCASCADE_FORCE

Backs out specified transactions, ignoring dependent transactions. Server runs undo SQL statements for specified transactions in reverse order of commit times.

If no constraints break and you are satisfied with the result, you can commit the changes; otherwise, you can roll them back.

NONCONFLICT_ONLY

Backs out changes to nonconflicting rows of the specified transactions. Database remains consistent, but transaction atomicity is lost.


TRANSACTION_BACKOUT analyzes the transactional dependencies, performs DML operations, and generates reports. TRANSACTION_BACKOUT does not commit the DML operations that it performs as part of transaction backout, but it holds all the required locks on rows and tables in the right form, preventing other dependencies from entering the system. To make the transaction backout permanent, you must explicitly commit the transaction.

TRANSACTION_BACKOUT Reports

To see the reports that TRANSACTION_BACKOUT generates, query the static data dictionary views *_FLASHBACK_TXN_STATE and *_FLASHBACK_TXN_REPORT.

*_FLASHBACK_TXN_STATE

The static data dictionary view *_FLASHBACK_TXN_STATE shows whether a transaction is active or backed out. If a transaction appears in this view, it is backed out.

*_FLASHBACK_TXN_STATE is maintained atomically for compensating transactions. If a compensating transaction is backed out, all changes that it made are also backed out, and *_FLASHBACK_TXN_STATE reflects this. For example, if compensating transaction ct backs out transactions t1 and t2, then t1 and t2 appear in *_FLASHBACK_TXN_STATE. If ct itself is later backed out, the effects of t1 and t2 are reinstated, and t1 and t2 disappear from *_FLASHBACK_TXN_STATE.

See Also:

Oracle Database Reference for more information about *_FLASHBACK_TXN_STATE

*_FLASHBACK_TXN_REPORT

The static data dictionary view *_FLASHBACK_TXN_REPORT provides a detailed report for each backed-out transaction.

See Also:

Oracle Database Reference for more information about *_FLASHBACK_TXN_REPORT

Using Flashback Data Archive (Oracle Total Recall)

A Flashback Data Archive provides the ability to track and store transactional changes to a table over its lifetime. A Flashback Data Archive is useful for compliance with record stage policies and audit reports.

A Flashback Data Archive consists of one or more tablespaces or parts thereof. You can have multiple Flashback Data Archives. If you are logged on as SYSDBA, you can specify a default Flashback Data Archive for the system. A Flashback Data Archive is configured with retention time. Data archived in the Flashback Data Archive is retained for the retention time.

By default, flashback archiving is off for any table. You can enable flashback archiving for a table if all of these conditions are true:

After flashback archiving is enabled for a table, you can disable it only if you either have the FLASHBACK ARCHIVE ADMINISTER system privilege or you are logged on as SYSDBA.

When choosing a Flashback Data Archive for a specific table, consider the data retention requirements for the table and the retention times of the Flashback Data Archives on which you have the FLASHBACK ARCHIVE object privilege.

Topics:

See Also:

http://www.oracle.com/database/total-recall.html for more information about Oracle Total Recall

Creating a Flashback Data Archive

Create a Flashback Data Archive with the CREATE FLASHBACK ARCHIVE statement, specifying:

  • Name of the Flashback Data Archive

  • Name of the first tablespace of the Flashback Data Archive

  • (Optional) Maximum amount of space that the Flashback Data Archive can use in the first tablespace

    The default is unlimited. Unless your space quota on the first tablespace is also unlimited, you must specify this value; otherwise, error ORA-55621 occurs.

  • Retention time (number of days that Flashback Data Archive data for the table is guaranteed to be stored)

If you are logged on as SYSDBA, you can also specify that this is the default Flashback Data Archive for the system. If you omit this option, you can still make this Flashback Data Archive the default later (see "Specifying the Default Flashback Data Archive").

Examples

  • Create a default Flashback Data Archive named fla1 that uses up to 10 G of tablespace tbs1, whose data are retained for one year:

    CREATE FLASHBACK ARCHIVE DEFAULT fla1 TABLESPACE tbs1
      QUOTA 10G RETENTION 1 YEAR;
    
  • Create a Flashback Data Archive named fla2 that uses tablespace tbs2, whose data are retained for two years:

    CREATE FLASHBACK ARCHIVE fla2 TABLESPACE tbs2 RETENTION 2 YEAR;
    

For more information about the CREATE FLASHBACK ARCHIVE statement, see Oracle Database SQL Language Reference.

Altering a Flashback Data Archive

With the ALTER FLASHBACK ARCHIVE statement, you can:

  • Change the retention time of a Flashback Data Archive

  • Purge some or all of its data

  • Add, modify, and remove tablespaces

    Note:

    Removing all tablespaces of a Flashback Data Archive causes an error.

If you are logged on as SYSDBA, you can also use the ALTER FLASHBACK ARCHIVE statement to make a specific file the default Flashback Data Archive for the system.

Examples

  • Make Flashback Data Archive fla1 the default Flashback Data Archive:

    ALTER FLASHBACK ARCHIVE fla1 SET DEFAULT;
    
  • To Flashback Data Archive fla1, add up to 5 G of tablespace tbs3:

    ALTER FLASHBACK ARCHIVE fla1 ADD TABLESPACE tbs3 QUOTA 5G;
    
  • To Flashback Data Archive fla1, add as much of tablespace tbs4 as needed:

    ALTER FLASHBACK ARCHIVE fla1 ADD TABLESPACE tbs4;
    
  • Change the maximum space that Flashback Data Archive fla1 can use in tablespace tbs3 to 20 G:

    ALTER FLASHBACK ARCHIVE fla1 MODIFY TABLESPACE tbs3 QUOTA 20G;
    
  • Allow Flashback Data Archive fla1 to use as much of tablespace tbs1 as needed:

    ALTER FLASHBACK ARCHIVE fla1 MODIFY TABLESPACE tbs1;
    
  • Change the retention time for Flashback Data Archive fla1 to two years:

    ALTER FLASHBACK ARCHIVE fla1 MODIFY RETENTION 2 YEAR;
    
  • Remove tablespace tbs2 from Flashback Data Archive fla1:

    ALTER FLASHBACK ARCHIVE fla1 REMOVE TABLESPACE tbs2;
    

    (Tablespace tbs2 is not dropped.)

  • Purge all historical data from Flashback Data Archive fla1:

    ALTER FLASHBACK ARCHIVE fla1 PURGE ALL;
    
  • Purge all historical data older than one day from Flashback Data Archive fla1:

    ALTER FLASHBACK ARCHIVE fla1
      PURGE BEFORE TIMESTAMP (SYSTIMESTAMP - INTERVAL '1' DAY);
    
  • Purge all historical data older than SCN 728969 from Flashback Data Archive fla1:

    ALTER FLASHBACK ARCHIVE fla1 PURGE BEFORE SCN 728969;
    

For more information about the ALTER FLASHBACK ARCHIVE statement, see Oracle Database SQL Language Reference.

Dropping a Flashback Data Archive

Drop a Flashback Data Archive with the DROP FLASHBACK ARCHIVE statement. Dropping a Flashback Data Archive deletes its historical data, but does not drop its tablespaces.

Example

Remove Flashback Data Archive fla1 and all its historical data, but not its tablespaces:

DROP FLASHBACK ARCHIVE fla1;

For more information about the DROP FLASHBACK ARCHIVE statement, see Oracle Database SQL Language Reference.

Specifying the Default Flashback Data Archive

By default, the system has no default Flashback Data Archive. If you are logged on as SYSDBA, you can specify default Flashback Data Archive in either of these ways:

  • Specify the name of an existing Flashback Data Archive in the SET DEFAULT clause of the ALTER FLASHBACK ARCHIVE statement. For example:

    ALTER FLASHBACK ARCHIVE fla1 SET DEFAULT;
    

    If fla1 does not exist, an error occurs.

  • Include DEFAULT in the CREATE FLASHBACK ARCHIVE statement when you create a Flashback Data Archive. For example:

    CREATE FLASHBACK ARCHIVE DEFAULT fla2 TABLESPACE tbs1
      QUOTA 10G RETENTION 1 YEAR;
    

The default Flashback Data Archive for the system is the default Flashback Data Archive for every user who does not have his or her own default Flashback Data Archive.

See Also:

Enabling and Disabling Flashback Data Archive

By default, flashback archiving is disabled for any table. You can enable flashback archiving for a table if you have the FLASHBACK ARCHIVE object privilege on the Flashback Data Archive to use for that table.

To enable flashback archiving for a table, include the FLASHBACK ARCHIVE clause in either the CREATE TABLE or ALTER TABLE statement. In the FLASHBACK ARCHIVE clause, you can specify the Flashback Data Archive where the historical data for the table are stored. The default is the default Flashback Data Archive for the system. If you specify a nonexistent Flashback Data Archive, an error occurs.

If you enable flashback archiving for a table, but AUM is disabled, error ORA-55614 occurs when you try to modify the table.

If a table has flashback archiving enabled, and you try to enable it again with a different Flashback Data Archive, an error occurs.

After flashback archiving is enabled for a table, you can disable it only if you either have the FLASHBACK ARCHIVE ADMINISTER system privilege or you are logged on as SYSDBA. To disable flashback archiving for a table, specify NO FLASHBACK ARCHIVE in the ALTER TABLE statement. (It is unnecessary to specify NO FLASHBACK ARCHIVE in the CREATE TABLE statement, because that is the default.)

See Also:

Oracle Database SQL Language Reference for more information about the FLASHBACK ARCHIVE clause of the CREATE TABLE statement, including restrictions on its use

Examples

  • Create table employee and store the historical data in the default Flashback Data Archive:

    CREATE TABLE employee (EMPNO NUMBER(4) NOT NULL, ENAME VARCHAR2(10),
      JOB VARCHAR2(9), MGR NUMBER(4)) FLASHBACK ARCHIVE;
    
  • Create table employee and store the historical data in the Flashback Data Archive fla1:

    CREATE TABLE employee (EMPNO NUMBER(4) NOT NULL, ENAME VARCHAR2(10),
      JOB VARCHAR2(9), MGR NUMBER(4)) FLASHBACK ARCHIVE fla1;
    
  • Enable flashback archiving for the table employee and store the historical data in the default Flashback Data Archive:

    ALTER TABLE employee FLASHBACK ARCHIVE;
    
  • Enable flashback archiving for the table employee and store the historical data in the Flashback Data Archive fla1:

    ALTER TABLE employee FLASHBACK ARCHIVE fla1;
    
  • Disable flashback archiving for the table employee:

    ALTER TABLE employee NO FLASHBACK ARCHIVE;
    

DDL Statements on Tables Enabled for Flashback Data Archive

Flashback Data Archive supports many DDL statements, including some that alter the table definition or move data. For example:

  • ALTER TABLE statement that does any of the following:

    • Adds, drops, renames, or modifies a column

    • Adds, drops, or renames a constraint

    • Drops or truncates a partition or subpartition operation

  • TRUNCATE TABLE statement

  • RENAME statement that renames a table

Some DDL statements cause error ORA-55610 when used on a table enabled for Flashback Data Archive. For example:

  • ALTER TABLE statement that includes an UPGRADE TABLE clause, with or without an INCLUDING DATA clause

  • ALTER TABLE statement that moves or exchanges a partition or subpartition operation

  • DROP TABLE statement

If you must use unsupported DDL statements on a table enabled for Flashback Data Archive, use the DBMS_FLASHBACK_ARCHIVE.DISASSOCIATE_FBA procedure to disassociate the base table from its Flashback Data Archive. To reassociate the Flashback Data Archive with the base table afterward, use the DBMS_FLASHBACK_ARCHIVE.REASSOCIATE_FBA procedure.

See Also:

Viewing Flashback Data Archive Data

Table 12-3 lists and briefly describes the static data dictionary views that you can query for information about Flashback Data Archive files.

Table 12-3 Static Data Dictionary Views for Flashback Data Archive Files

View Description

*_FLASHBACK_ARCHIVE

Displays information about Flashback Data Archive files.

*_FLASHBACK_ARCHIVE_TS

Displays tablespaces of Flashback Data Archive files.

*_FLASHBACK_ARCHIVE_TABLES

Displays information about tables that are enabled for Data Flashback Archive files.


See Also:

Flashback Data Archive Scenarios

Scenario: Using Flashback Data Archive to Enforce Digital Shredding

Your company wants to "shred" (delete) historical data changes to the Taxes table after ten years. When you create the Flashback Data Archive for Taxes, you specify a retention time of ten years:

CREATE FLASHBACK ARCHIVE taxes_archive TABLESPACE tbs1 RETENTION 10 YEAR;

When history data from transactions on Taxes exceeds the age of ten years, it is purged. (The Taxes table itself, and history data from transactions less than ten years old, are not purged.)

Scenario: Using Flashback Data Archive to Access Historical Data

You want to be able to retrieve the inventory of all items at the beginning of the year from the table inventory, and to be able to retrieve the stock price for each symbol in your portfolio at the close of business on any specified day of the year from the table stock_data.

Create a default Flashback Data Archive named fla1 that uses up to 10 G of tablespace tbs1, whose data are retained for five years (you must be logged on as SYSDBA):

CREATE FLASHBACK ARCHIVE DEFAULT fla1 TABLESPACE tbs1
  QUOTA 10G RETENTION 5 YEAR;

Enable Flashback Data Archive for the tables inventory and stock_data, and store the historical data in the default Flashback Data Archive:

ALTER TABLE inventory FLASHBACK ARCHIVE;
ALTER TABLE stock_data FLASHBACK ARCHIVE;

To retrieve the inventory of all items at the beginning of the year 2007, use this query:

SELECT product_number, product_name, count FROM inventory AS OF
  TIMESTAMP TO_TIMESTAMP ('2007-01-01 00:00:00', 'YYYY-MM-DD HH24:MI:SS');

To retrieve the stock price for each symbol in your portfolio at the close of business on July 23, 2007, use this query:

SELECT symbol, stock_price FROM stock_data AS OF
  TIMESTAMP TO_TIMESTAMP ('2007-07-23 16:00:00', 'YYYY-MM-DD HH24:MI:SS')
  WHERE symbol IN my_portfolio;

Scenario: Using Flashback Data Archive to Generate Reports

You want users to be able to generate reports from the table investments, for data stored in the past five years.

Create a default Flashback Data Archive named fla2 that uses up to 20 G of tablespace tbs1, whose data are retained for five years (you must be logged on as SYSDBA):

CREATE FLASHBACK ARCHIVE DEFAULT fla2 TABLESPACE tbs1
  QUOTA 20G RETENTION 5 YEAR;

Enable Flashback Data Archive for the table investments, and store the historical data in the default Flashback Data Archive:

ALTER TABLE investments FLASHBACK ARCHIVE;

Lisa wants a report on the performance of her investments at the close of business on December 31, 2006. She uses this query:

SELECT * FROM investments AS OF
  TIMESTAMP TO_TIMESTAMP ('2006-12-31 16:00:00', 'YYYY-MM-DD HH24:MI:SS')
  WHERE name = 'LISA';

Scenario: Using Flashback Data Archive for Auditing

A medical insurance company must audit a medical clinic. The medical insurance company has its claims in the table Billings, and creates a default Flashback Data Archive named fla4 that uses up to 100 G of tablespace tbs1, whose data are retained for 10 years:

CREATE FLASHBACK ARCHIVE DEFAULT fla4 TABLESPACE tbs1
  QUOTA 100G RETENTION 10 YEAR;

The company enables Flashback Data Archive for the table Billings, and stores the historical data in the default Flashback Data Archive:

ALTER TABLE Billings FLASHBACK ARCHIVE;

On May 1, 2007, clients were charged the wrong amounts for some diagnoses and tests. To see the records as of May 1, 2007, the company uses this query:

SELECT date_billed, amount_billed, patient_name, claim_Id,
  test_costs, diagnosis FROM Billings AS OF TIMESTAMP
  TO_TIMESTAMP('2007-05-01 00:00:00', 'YYYY-MM-DD HH24:MI:SS');

Scenario: Using Flashback Data Archive to Recover Data

An end user recovers from erroneous transactions that were previously committed in the database. The undo data for the erroneous transactions is no longer available, but because the required historical information is available in the Flashback Data Archive, Flashback Query works seamlessly.

Lisa manages a software development group whose product sales are doing well. On November 3, 2007, she decides to give all her level-three employees who have more than two years of experience a salary increase of 10% and a promotion to level four. Lisa asks her HR representative, Bob, to make the changes.

Using the HR web application, Bob updates the employee table to give Lisa's level-three employees a 10% raise and a promotion to level four. Then Bob finishes his work for the day and leaves for home, unaware that he omitted the requirement of two years of experience in his transaction. A few days later, Lisa checks to see if Bob has done the updates and finds that everyone in the group was given a raise! She calls Bob immediately and asks him to correct the error.

At first, Bob thinks he cannot return the employee table to its prior state without going to the backups. Then he remembers that the employee table has Flashback Data Archive enabled.

First, he verifies that no other transaction modified the employee table after his: The commit time stamp from the transaction query corresponds to Bob's transaction, two days ago.

Next, Bob uses these statements to return the employee table to the way it was before his erroneous change:

DELETE EMPLOYEE WHERE MANAGER = 'LISA JOHNSON';
INSERT INTO EMPLOYEE
  SELECT * FROM EMPLOYEE
    AS OF TIMESTAMP (SYSTIMESTAMP - INTERVAL '2' DAY)
      WHERE MANAGER = 'LISA JOHNSON';

Bob then reexecutes the update that Lisa had requested.

General Guidelines for Oracle Flashback Technology

Performance Guidelines for Oracle Flashback Technology