Considerations for retained locks and record table full conditions

The CF lock structure includes two parts:

a lock table, used to determine whether there is R/W interest among systems on a particular resource
record table space to keep track of information for retained locks and spheres which have been processed by VSAM RLS

If a commit protocol application such as CICS® fails, the locks protecting updates against recoverable spheres are remembered in the record table space until CICS performs the required backouts. Also, update locks associated with indoubt transactions are remembered until the indoubts are resolved.

When used record table space reaches 80% or greater, informational message IGW326I is issued. A shortage of record table space can occur for the following reasons:

The size of the lock structure is too small for normal system operation.
A CICS system has failed and cannot be successfully restarted to run its backouts. As a consequence, record table space cannot be freed up.
Outstanding indoubt transactions exist. CICS provides commands to display indoubt transactions and resolve them.
Transactions are in backout failed state. This means that the backouts could not complete and free record table space.

Because it might be difficult to remedy these situations quickly, you should respond to a record table shortage by modifying the CFRM policy to increase the size of the lock structure, in order to provide additional record table space and increase the space available for retained locks. Then, activate that policy and rebuild the lock structure by operator command. The operator command can be used to change the size of the lock structure.

You can increase record table space by carefully selecting the total lock memory allocation quantity. Record table space is guaranteed to never be less than one-half of the total lock space allocated to RLS, but it can be more if the total size is not a power of two. A lock space allocation of 32 MB causes 16 MB to be allocated to the lock table and 16 MB to be allocated to the record lock table. An allocation of 63 MB, on the other hand, causes 16MB to be allocated to the lock table, and all of the remaining memory (for example. 47 MB) is then allocated to the record table space. Thus, selecting a total lock size that is not a power of two value is a means of causing the record space to grow without necessarily increasing the table size.

When you attempt to change the size of the lock structure using either the rebuild or the alter function and the record table size is greater than 50%, VSAM RLS will determine whether the new table has enough space for all existing record table entries, plus enough empty space for future locking processes (120%). If the answer is no, message IGW322I is displayed. A rebuild request is rejected; an alter request proceeds.

If the record table becomes full, VSAM requests which require that a lock be recorded receive RPL feedback, and CICS backs out the transaction. A record table full condition means that transactions cannot complete successfully, and the size of the lock structure must be increased.