Planning your structures
A queue-sharing group requires a minimum of two structures to be defined. The first structure, known as the administrative structure, is used to coordinate WebSphere MQ internal activity across the queue-sharing group. No user data is held in this structure. It has a fixed name of qsg-nameCSQ_ADMIN (where qsg-name is the name of your queue-sharing group). Subsequent structures are used to hold the messages on WebSphere MQ shared queues. Each structure can hold up to 512 shared queues.
Using multiple structures
A queue-sharing group can connect to up to 64 Coupling Facility structures. One of these structures must be the administration structure, but we can use up to 63 structures for WebSphere MQ data. You might choose to use multiple structures for any of the following reasons:
- You have some queues that are likely to hold a very large number of messages and so require all the resources of an entire Coupling Facility.
- You have a requirement for a very large number of shared queues, so they must be split across multiple structures because each structure can contain only 512 queues.
- RMF reports on the usage characteristic of a structure suggest that you should distribute the queues it contains across a number of Coupling Facilities.
- You want some queue data to held in a physically different Coupling Facility from other queue data for data isolation reasons.
- Recovery of persistent shared messages is performed using structure level attributes and commands, for example BACKUP CFSTRUCT. To simplify backup and recovery, you could assign queues that hold nonpersistent messages to different structures from those that hold persistent messages.
When choosing which Coupling Facilities to allocate the structures in, consider the following points:
- Your data isolation requirements.
- The volatility of the Coupling Facility (that is, its ability to preserve data through a power outage).
- Failure independence between the accessing systems and the Coupling Facility, or between Coupling Facilities.
- The level of Coupling Facility Control Code (CFCC) installed on the Coupling Facility (WebSphere MQ requires Level 9 or higher).