Managing logs
You need to manage linear logs yourself. However, circular logs are nearly self-managing, but sometimes need intervention to resolve space problems.
On circular logging, the queue manager reclaims freed space in the log files. This activity is not apparent to the user, and you do not usually see the amount of disk space used reduce, because the space allocated is quickly reused.
On linear logging, the log might fill if a checkpoint has not been taken for a long time, or if a long-running transaction wrote a log record a long time ago. The queue manager tries to take checkpoints often enough to avoid the first problem.
If the log fills, message AMQ7463 is issued. In addition, if the
log fills because a long-running transaction has prevented the space being released, message
AMQ7465 is issued.
Of the log records, only those written since the start of the last complete checkpoint, and those written by any active transactions, are needed to restart the queue manager.
Over time, the oldest log records written become unnecessary for restarting the queue manager.
When a long-running transaction is detected, activity is scheduled to asynchronously rollback that transaction. If, for some unexpected reason, that asynchronous rollback were to fail, some MQI calls return MQRC_RESOURCE_PROBLEM in that situation.
Note that space is reserved to commit or roll back all in-flight transactions, so MQCMIT or MQBACK should not fail.
The queue manager rolls back transactions that run for a long duration. An application that has a transaction is rolled back in this way cannot perform subsequent MQPUT or MQGET operations specifying sync point under the same transaction.
However, transactions ended manually start a new log. Note, that whereas new log space is allocated immediately, log space that has been released takes a finite time to be freed up.
An attempt to put or get a message under sync point in this state returns MQRC_BACKED_OUT. The application can then issue MQCMIT, which returns MQRC_BACKED_OUT, or MQBACK and start a new transaction. When the transaction consuming too much log space has been rolled back, the log space is released and the queue manager continues to operate normally.