Structure duplex support behavior with a secondary cluster caching facility

When running in a highly available environment, you must use multiple cluster caching facilities to provide continuous support if a cluster caching facility, also known as a CF, goes down.

The following structures are supported by the cluster caching facility:
  • The group buffer pool (GBP)
  • The CF lock manager (LOCK)
  • The shared communication area (SCA).

The primary and secondary CF servers share the same host configuration in a highly available environment. It is recommended that host specifications such as CPU speed, number of CPUs, and the amount of random access memory (RAM) are the same for both CF servers. The two CF servers share one set of configuration parameters and access the same port numbers.

The CF has configurable structures, the GBP, LOCK, and SCA. Each structure supports online updates. When increasing the allotted memory for these structures, also known as growing a structure, the request is first sent to the secondary CF server and then to the primary CF server. The reverse is true when decreasing the allotted memory for these structures, also known as shrinking a structure. The shrinking request is first sent to the primary CF server and then to the secondary CF server. A structure in the secondary CF is always as big or bigger than the structure in the primary CF to ensure there are no storage issues after a CF failover.

If either the primary CF or secondary CF fails to update a CF configuration parameter, the other CF rolls back to the previous setting for that CF configuration parameter. This rollback ensures that there is sufficient structure memory available on both CFs.

By default, a resize request waits until the resizing operation completes before returning to the client. If you interrupt the resize request with a user control action, such as Ctrl+C, the resizing operation is cancelled on bothCFs. The size of the structure on the secondary CF is then adjusted to match the value that is on the primary CF. You can monitor a resize request by running the command DB2 GET DB CFG SHOW DETAIL.