Message persistence FAQs

Answer

A1. Nonpersistent messages do not survive restarts because they are considered to be nonessential messages. However the queue attribute NPMCLASS(HIGH) can change the treatment of non-persistent messages (see details below).

A2. Persistent messages survive system restarts because they are considered to be essential messages. If the data in a message is important to your business, then you should always make your messages persistent.

A3. Set MQMD message persistence to persistent (MQPER_PERSISTENT), or nonpersistent (MQPER_NOT_PERSISTENT) and your message will always retain that value.

Note: MQPER_PERSISTENCE_AS_Q_DEF is the default setting for the persistence value in the MQMD. See the persistence values listed below.

A4. Yes, you can lose nonpersistent messages on a fast channel because they are not logged.

• Persistent messages are logged. Logging messages reduces the performance of your application, so you should use persistent messages for essential data only.
• If the data in a message can be discarded when a queue manager stops or fails, use a nonpersistent message.

Diagnostic hints and tips:

1. If you suspect that you are losing messages, or if you want to verify the persistence setting for your application's messages. Trace your application putting a message to the destination queue, or browse messages on the queue.
2. Examine the MQMD - Message descriptor fields and verify the persistence setting.
3. The queue attribute NPMCLASS(HIGH) can change the treatment of non-persistent messages on a 'normal' queue manager restart. The queue manager attempts to retain non-persistent messages on this queue over a queue manager restart. Note that you cannot set this parameter on z/OS.

See Non Persistent Message Class (NPMCLASS)

Additional information

MQPER_PERSISTENCE_AS_Q_DEF can lead to unexpected results. If there is more than one definition in the queue-name resolution path, the default persistence attribute is taken from first queue definition in the path at the time of the MQPUT or MQPUT1 call. This queue could be an:

• alias queue
• local queue
• local definition of a remote queue
• queue-manager alias
• transmission queue
• cluster queue