Db2 IRLM Lock Structure Help

The Db2 IRLM coupling facility lock structure contains information used to determine cross-system contention on a particular resource. There is one lock structure per data sharing group used by IRLM to control locking. It contains information about locks that are currently used to control changes to shared resources. The size of the lock structure must reflect the total number of concurrent locks held by all members in the Db2 data sharing group.

The size of the Db2 IRLM lock structure is a function of the number of systems sharing the lock structure, the number of table spaces associated with the data sharing group, and the lock rate.

Lock Rate

Maximum locking rate per second. The lock rate information should be obtained from a Db2 Performance Monitor(or equivalent) batch statistics report under the Locking Section. It is the sum of the Lock Requests, Unlock Requests, and Change Requests. The statistics report should be run for a peak online hour and peak batch hour to come up with the capacity value.

Number of Systems

The maximum number of systems expected to be active in the sysplex at any one time.

Number of Table Spaces

Total number of table spaces associated with all the databases managed by the data sharing group.

Max Number of Users

The maximum number of users of the lock structure, from the MAXUSRS value specified in the IRLMPROC procedure.

Max Number of Connectors

The maximum number of connectors per structure specified when the primary CFRM couple data set was formatted (ITEM NAME(CONNECT) NUMBER(xx)). CFSizer will use the smaller of this number or the release-specific maximum number of systems in a sysplex. If you bring into use a new primary CFRM couple data set formatted for a greater number of connectors per structure, you must repeat this calculation, since the new value will be applied if you rebuild the structure or re-IPL the sysplex.

Asynchronous Duplexing

Use this input parameter to indicate whether the structure will be eligible for asynchronous duplexing. If the CFRM policy description for this structure specifies

DUPLEX(ALLOWED|ENABLED,dupoptions)

where dupoptions includes ASYNC or ASYNCONLY, then specify YES. Otherwise, specify NO.

The lock structure storage is allocated partly to lock table entries (LTEs) and partly to record list entries (RLEs). Database operations can fail if the structure contains an insufficient number of either. IRLM reserves space for "must complete" functions (such as rollbacks or commit processing) so that a shortage of storage will not cause a Db2 subsystem failure. To ensure that the structure storage is allocated appropriately, IBM recommends that installations specify the number of LTEs to be contained by the structure on the procedure used to start IRLM (irlmproc). Specifying a CFRM policy size much larger than CFSizer's recommendation without specifying the number of LTEs on the irlmproc can cause the structure to be allocated without sufficient RLEs. CFSizer models the number of LTEs as

(lock rate + (number of systems) * (number of table spaces)) * 200

Note that the system will round the calculated number of LTEs up to the next highest power of 2.

For more information, see Installing, migrating and enabling Db2 data sharing in IBM Knowledge Center.