Non-RLS provides local locking (within the scope of a single buffer pool) of the VSAM control interval. Locking contention can result in an “exclusive control conflict” error response to a VSAM record management request.

VSAM RLS uses a DFSMS lock manager to provide a system-managed duplexing rebuild process. The locking granularity is at the VSAM record level. When contention occurs on a VSAM record, the request that encountered the contention waits for the contention to be removed. The DFSMS lock manager provides deadlock detection. When a lock request is in deadlock, VSAM rejects the request. This results in the VSAM record management request completing with a deadlock error response.

When you request a user-managed rebuild for a lock structure, the validity check function determines if there is enough space for the rebuild process to complete. If there is not enough space, the system rejects the request and displays an informational message.

When you request an alter operation for a lock structure, the validity check function determines if there is enough space for the alter process to complete. If there is not enough space, the system displays a warning message that includes the size recommendation.

VSAM RLS supports a timeout value that you can specify through the RPL, in the PARMLIB, or in the JCL. CICS uses this parameter to ensure that a transaction does not wait indefinitely for a lock to become available. VSAM RLS uses a timeout function of the DFSMS lock manager.

When an ESDS is used with VSAM RLS, to serialize the processing of ESDS records, an exclusive, sysplex-wide data-set level "add to end" lock is held each time a record is added to the end of the data set. Reading and updating of existing records do not acquire the lock. Non-RLS VSAM does not need such serialization overhead because it does not serialize ESDS record additions across the sysplex.

Recommendation: Carefully design your use of ESDS with RLS; otherwise, you might see performance differences between accessing ESDSs with and without RLS.