Online migration

Queue files can be migrated while the queue manager is running. This is known as online migration.

Online migrations are done in exactly the same way as offline migrations. During the migration the queue manager knows that, temporarily, the queue being migrated is represented by two physical queue files, potentially with a different number of partitions. All new messages go into the new queue file. Old messages are looked for in the old file first, if not found (because they have already been moved by the migration process) the queue manager looks for the message in the new queue file. Since all queue files are TMF protected, no inconsistencies can arise.

The I/O load for a queue being migrated is significantly higher than under normal circumstances. However, this should only be a concern if the queue to be migrated is very large (more than 10000 messages, or a large number of large messages). Queues with less than 10000 messages of size less than 25k are typically migrated within a few seconds.

If the queue manager is ended while online migrations are in process, the migrations are interrupted. When the queue manager is started again, all migrations continue automatically.

While using online migration, the MQOPEN options MQOO_SET and MQOO_BROWSE must be allowed against the migrating queues.