Where are shared queue messages held?
Messages that are put onto shared queues are not stored on page sets and do not use buffer pools.
The messages in shared queues have entries on list structures in the zSeries Coupling Facility. Many queue managers in the same sysplex can access those messages.
Shared queue messages of size less than or equal to 63KB are held entirely in the CF list structure defined for that queue.
Shared queue messages of size greater than 63KB have their message data held as one or more binary large objects (BLOBs) in a DB2 table which is shared by a DB2 data sharing group.
Messages put on a shared queue are stored in a Coupling Facility structure until they are retrieved by an MQGET. Coupling Facility operations are used to:
- search for the next retrievable message
- lock uncommitted messages on shared queues
- notify interested queue managers about the arrival of committed messages
MQPUT and MQGET operations on persistent messages are recorded on the log of the queue manager performing that operation. This minimizes the risk of data loss in the event of a Coupling Facility failure.