111 DBMS_TRANSACTION

The DBMS_TRANSACTION package provides access to SQL transaction statements from stored procedures.

Using DBMS_TRANSACTION

Security Model

Security Model

This package runs with the privileges of calling user, rather than the package owner SYS.

Summary of DBMS_TRANSACTION Subprograms

Table 111-1 DBMS_TRANSACTION Package Subprograms

Subprogram	Description
ADVISE_COMMIT Procedure	Equivalent to the SQL statement: `ALTER SESSION ADVISE COMMIT`
ADVISE_NOTHING Procedure	Equivalent to the SQL statement: `ALTER SESSION ADVISE NOTHING`
ADVISE_ROLLBACK Procedure	Equivalent to the SQL statement: `ALTER SESSION ADVISE ROLLBACK`
BEGIN_DISCRETE_TRANSACTION Procedure	Sets "discrete transaction mode" for this transaction
COMMIT Procedure	Equivalent to the SQL statement: `COMMIT`
COMMIT_COMMENT Procedure	Equivalent to the SQL statement: `COMMIT COMMENT <text>`
COMMIT_FORCE Procedure	Equivalent to the SQL statement: `COMMIT FORCE <text>, <number>"`
LOCAL_TRANSACTION_ID Function	Returns the local (to instance) unique identifier for the current transaction
PURGE_LOST_DB_ENTRY Procedure	Enables removal of incomplete transactions from the local site when the remote database is destroyed or re-created before recovery completes
PURGE_MIXED Procedure	Deletes information about a given mixed outcome transaction
READ_ONLY Procedure	Equivalent to the SQL statement: `SET TRANSACTION READ ONLY`
READ_WRITE Procedure	equivalent to the SQL statement: `SET TRANSACTION READ WRITE`
ROLLBACK Procedure	Equivalent to the SQL statement: `ROLLBACK`
ROLLBACK_FORCE Procedure	Equivalent to the SQL statement: `ROLLBACK` `FORCE` `<text>`
ROLLBACK_SAVEPOINT Procedure	Equivalent to the SQL statement: `ROLLBACK` `TO` `SAVEPOINT` `<savepoint_name>`
SAVEPOINT Procedure	Equivalent to the SQL statement: `SAVEPOINT` `<savepoint_name>`
STEP_ID Function	Returns local (to local transaction) unique positive integer that orders the DML operations of a transaction
USE_ROLLBACK_SEGMENT Procedure	Equivalent to the SQL statement: `SET` `TRANSACTION` `USE` `ROLLBACK` `SEGMENT` `<rb_seg_name>`

ADVISE_COMMIT Procedure

This procedure is equivalent to the SQL statement:

ALTER SESSION ADVISE COMMIT

Syntax

DBMS_TRANSACTION.ADVISE_COMMIT;

ADVISE_NOTHING Procedure

This procedure is equivalent to the SQL statement:

ALTER SESSION ADVISE NOTHING

Syntax

DBMS_TRANSACTION.ADVISE_NOTHING;

ADVISE_ROLLBACK Procedure

This procedure is equivalent to the SQL statement:

ALTER SESSION ADVISE ROLLBACK

Syntax

DBMS_TRANSACTION.ADVISE_ROLLBACK;

BEGIN_DISCRETE_TRANSACTION Procedure

This procedure sets "discrete transaction mode" for this transaction.

Syntax

DBMS_TRANSACTION.BEGIN_DISCRETE_TRANSACTION;

Exceptions

Table 111-2 BEGIN_DISCRETE_TRANSACTION Procedure Exceptions

Exception Description

Exception	Description
`ORA-08175`	A transaction attempted an operation which cannot be performed as a discrete transaction. If this exception is encountered, then rollback and retry the transaction
`ORA-08176`	A transaction encountered data changed by an operation that does not generate rollback data: create index, direct load or discrete transaction. If this exception is encountered, then retry the operation that received the exception.

ORA-08175

A transaction attempted an operation which cannot be performed as a discrete transaction.

If this exception is encountered, then rollback and retry the transaction

ORA-08176

A transaction encountered data changed by an operation that does not generate rollback data: create index, direct load or discrete transaction.

If this exception is encountered, then retry the operation that received the exception.

Examples

DISCRETE_TRANSACTION_FAILED exception;
    pragma exception_init(DISCRETE_TRANSACTION_FAILED, -8175);
CONSISTENT_READ_FAILURE exception;
    pragma exception_init(CONSISTENT_READ_FAILURE, -8176);

COMMIT Procedure

This procedure is equivalent to the SQL statement:

COMMIT

This procedure is included for completeness, the functionality being already implemented as part of PL/SQL.

Syntax

DBMS_TRANSACTION.COMMIT;

COMMIT_COMMENT Procedure

This procedure is equivalent to the SQL statement:

COMMIT COMMENT <text>

Syntax

DBMS_TRANSACTION.COMMIT_COMMENT (
   cmnt VARCHAR2);

Parameters

Table 111-3 COMMIT_COMMENT Procedure Parameters

Parameter	Description
`cmnt`	Comment to associate with this commit.

COMMIT_FORCE Procedure

This procedure is equivalent to the SQL statement:

COMMIT FORCE <text>, <number>"

Syntax

DBMS_TRANSACTION.COMMIT_FORCE (
   xid VARCHAR2, 
   scn VARCHAR2 DEFAULT NULL);

Parameters

Table 111-4 COMMIT_FORCE Procedure Parameters

Parameter	Description
`xid`	Local or global transaction ID.
`scn`	System change number.

LOCAL_TRANSACTION_ID Function

This function returns the local (to instance) unique identifier for the current transaction. It returns null if there is no current transaction.

Syntax

DBMS_TRANSACTION.LOCAL_TRANSACTION_ID (
   create_transaction BOOLEAN := FALSE)
  RETURN VARCHAR2;

Parameters

Table 111-5 LOCAL_TRANSACTION_ID Function Parameters

Parameter	Description
`create_transaction`	If true, then start a transaction if one is not currently active.

PURGE_LOST_DB_ENTRY Procedure

When a failure occurs during commit processing, automatic recovery consistently resolves the results at all sites involved in the transaction. However, if the remote database is destroyed or re-created before recovery completes, then the entries used to control recovery in DBA_2PC_PENDING and associated tables are never removed, and recovery will periodically retry. Procedure PURGE_LOST_DB_ENTRY enables removal of such transactions from the local site.

Syntax

DBMS_TRANSACTION.PURGE_LOST_DB_ENTRY (
   xid VARCHAR2);

Parameters

Table 111-6 PURGE_LOST_DB_ENTRY Procedure Parameters

Parameter	Description
`xid`	Must be set to the value of the `LOCAL_TRAN_ID` column in the `DBA_2PC_PENDING` table.

Usage Notes

WARNING:

PURGE_LOST_DB_ENTRY should only be used when the other database is lost or has been re-created. Any other use may leave the other database in an unrecoverable or inconsistent state.

Before automatic recovery runs, the transaction may show up in DBA_2PC_PENDING as state "collecting", "committed", or "prepared". If the DBA has forced an in-doubt transaction to have a particular result by using "commit force" or "rollback force", then states "forced commit" or "forced rollback" may also appear. Automatic recovery normally deletes entries in any of these states. The only exception is when recovery finds a forced transaction which is in a state inconsistent with other sites in the transaction; in this case, the entry is left in the table and the MIXED column has the value 'yes'.

However, under certain conditions, it may not be possible for automatic recovery to run. For example, a remote database may have been permanently lost. Even if it is re-created, it gets a new database ID, so that recovery cannot identify it (a possible symptom is ORA-02062). In this case, the DBA may use the procedure PURGE_LOST_DB_ENTRY to clean up the entries in any state other than "prepared". The DBA does not need to be in any particular hurry to resolve these entries, because they are not holding any database resources.

The following table indicates what the various states indicate about the transaction and what the DBA actions should be:

Table 111-7 PURGE_LOST_DB_ENTRY Procedure States

State of Column	State of Global Transaction	State of Local Transaction	Normal DBA Action	Alternative DBA Action
`Collecting`	`Rolled back`	`Rolled back`	`None`	`PURGE_LOST_DB_ENTRY (See Note 1)`
`Committed`	`Committed`	`Committed`	`None`	`PURGE_LOST_DB_ENTRY (See Note 1)`
`Prepared`	`Unknown`	`Prepared`	`None`	`FORCE COMMIT or ROLLBACK`
`Forced commit`	`Unknown`	`Committed`	`None`	`PURGE_LOST_DB_ENTRY (See Note 1)`
`Forced rollback`	`Unknown`	`Rolled back`	`None`	`PURGE_LOST_DB_ENTRY (See Note 1)`
`Forced commit (mixed)`	`Mixed`	`Committed`	`(See Note 2)`
`Forced rollback (mixed)`	`Mixed`	`Rolled back`	`(See Note 2)`

NOTE 1:

Use only if significant reconfiguration has occurred so that automatic recovery cannot resolve the transaction. Examples are total loss of the remote database, reconfiguration in software resulting in loss of two-phase commit capability, or loss of information from an external transaction coordinator such as a TP monitor.

NOTE 2:

Examine and take any manual action to remove inconsistencies; then use the procedure PURGE_MIXED.

PURGE_MIXED Procedure

When in-doubt transactions are forced to commit or rollback (instead of letting automatic recovery resolve their outcomes), there is a possibility that a transaction can have a mixed outcome: Some sites commit, and others rollback. Such inconsistency cannot be resolved automatically by Oracle; however, Oracle flags entries in DBA_2PC_PENDING by setting the MIXED column to a value of 'yes'.

Oracle never automatically deletes information about a mixed outcome transaction. When the application or DBA is certain that all inconsistencies that might have arisen as a result of the mixed transaction have been resolved, this procedure can be used to delete the information about a given mixed outcome transaction.

Syntax

DBMS_TRANSACTION.PURGE_MIXED (
   xid VARCHAR2);

Parameters

Table 111-8 PURGE_MIXED Procedure Parameters

Parameter	Description
`xid`	Must be set to the value of the `LOCAL_TRAN_ID` column in the `DBA_2PC_PENDING` table.

READ_ONLY Procedure

This procedure is equivalent to the SQL statement:

SET TRANSACTION READ ONLY

Syntax

DBMS_TRANSACTION.READ_ONLY;

READ_WRITE Procedure

This procedure is equivalent to the SQL statement:

SET TRANSACTION READ WRITE

Syntax

DBMS_TRANSACTION.READ_WRITE;

ROLLBACK Procedure

This procedure is equivalent to the SQL statement:

ROLLBACK

This procedure is included for completeness, the functionality being already implemented as part of PL/SQL.

Syntax

DBMS_TRANSACTION.ROLLBACK;

ROLLBACK_FORCE Procedure

This procedure is equivalent to the SQL statement:

ROLLBACK FORCE <text>

Syntax

DBMS_TRANSACTION.ROLLBACK_FORCE (
   xid VARCHAR2);

Parameters

Table 111-9 ROLLBACK_FORCE Procedure Parameters

Parameter	Description
`xid`	Local or global transaction ID.

ROLLBACK_SAVEPOINT Procedure

This procedure is equivalent to the SQL statement:

ROLLBACK TO SAVEPOINT <savepoint_name>

This procedure is included for completeness, the functionality being already implemented as part of PL/SQL.

Syntax

DBMS_TRANSACTION.ROLLBACK_SAVEPOINT (
   savept VARCHAR2);

Parameters

Table 111-10 ROLLBACK_SAVEPOINT Procedure Parameters

Parameter	Description
`savept`	Savepoint identifier.

SAVEPOINT Procedure

This procedure is equivalent to the SQL statement:

SAVEPOINT <savepoint_name>

This procedure is included for completeness, the feature being already implemented as part of PL/SQL.

Syntax

DBMS_TRANSACTION.SAVEPOINT (
   savept VARCHAR2);

Parameters

Table 111-11 SAVEPOINT Procedure Parameters

Parameter	Description
`savept`	Savepoint identifier.

STEP_ID Function

This function returns local (to local transaction) unique positive integer that orders the DML operations of a transaction.

Syntax

DBMS_TRANSACTION.STEP_ID 
   RETURN NUMBER;

USE_ROLLBACK_SEGMENT Procedure

This procedure is equivalent to the SQL statement:

SET TRANSACTION USE ROLLBACK SEGMENT <rb_seg_name>

Syntax

DBMS_TRANSACTION.USE_ROLLBACK_SEGMENT (
   rb_name VARCHAR2);

Parameters

Table 111-12 USE_ROLLBACK_SEGMENT Procedure Parameters

Parameter	Description
`rb_name`	Name of rollback segment to use.