Simulating Distributed Transaction Failure

Forcing a Distributed Transaction to Fail

You can include comments in the COMMENT parameter of the COMMIT statement. To intentionally induce a failure during the two-phase commit phases of a distributed transaction, include the following comment in the COMMENT parameter:

COMMIT COMMENT 'ORA-2PC-CRASH-TEST-n';

where n is one of the following integers:

For example, the following statement returns the following messages if the local commit point strength is greater than the remote commit point strength and both nodes are updated:

COMMIT COMMENT 'ORA-2PC-CRASH-TEST-7';

ORA-02054: transaction 1.93.29 in-doubt
ORA-02059: ORA_CRASH_TERST_7 in commit comment

At this point, the in-doubt distributed transaction appears in the DBA_2PC_PENDING view. If enabled, RECO automatically resolves the transaction.

Disabling and Enabling RECO

The RECO background process of an Oracle Database instance automatically resolves failures involving distributed transactions. At exponentially growing time intervals, the RECO background process of a node attempts to recover the local portion of an in-doubt distributed transaction.

RECO can use an existing connection or establish a new connection to other nodes involved in the failed transaction. When a connection is established, RECO automatically resolves all in-doubt transactions. Rows corresponding to any resolved in-doubt transactions are automatically removed from the pending transaction table of each database.

You can enable and disable RECO using the ALTER SYSTEM statement with the ENABLE/DISABLE DISTRIBUTED RECOVERY options. For example, you can temporarily disable RECO to force the failure of a two-phase commit and manually resolve the in-doubt transaction.

The following statement disables RECO:

ALTER SYSTEM DISABLE DISTRIBUTED RECOVERY;

Alternatively, the following statement enables RECO so that in-doubt transactions are automatically resolved:

ALTER SYSTEM ENABLE DISTRIBUTED RECOVERY;