Transaction Management

The following sections address issues in managing transactions.

Storing Transaction Data and Performance

To improve performance, Message Queue brokers are configured by default to use a memory-mapped file to store transaction data. On file systems that do not support memory-mapped files, you can disable this behavior by setting the broker property imq.persist.file.transaction.memorymappedfile.enabled to false.

Rolling Back Transactions

Previously, only transactions in a PREPARED state were allowed to be rolled back administratively. That is, if a session that was part of a distributed transaction did not terminate gracefully, the transaction remained in a state that could not be cleaned up by the broker administrator. In Message Queue 3.7 UR1 or 3. 7 UR2 you can use the imqcmd utility to clean up (roll back) transactions that are in the following states: STARTED, FAILED, INCOMPLETE, COMPLETE, PREPARED.

To help you determine whether a particular transaction can be rolled back (especially when it is not in a PREPARED state), the imqcmd utility provides additional data as part of the imqcmd query txn output: it provides the connection id for the connection that started the transaction and specifies the time when the transaction was created. Using this information, the administrator can decide whether the transaction needs to be rolled back. In general, the administrator should avoid rolling back a transaction prematurely.