RLS Record level locking
Files opened in RLS mode can be accessed by many CICS® regions simultaneously. This means that it is impractical for the individual CICS regions to attempt to control record locking, and therefore VSAM maintains a single central lock structure using the lock-assist mechanism of the MVS™ coupling facility.
This central lock structure provides sysplex-wide locking at a record level—control interval (CI) locking is not used. This is in contrast to the locks for files in non-RLS mode, the scope of which is limited to a single CICS region, and that are either CI locks or CICS ENQs.
Record locks within RLS are owned by a named UOW within a named CICS region. The lock owner name is the APPLID of the CICS region, plus the UOW ID. For example, when CICS makes a request that can create a lock, CICS passes to VSAM the UOW ID. This enables VSAM to build the lock name using the UOW ID, the record key, and the name of the CICS region.
CICS releases all locks on completion of a UOW using a VSAM interface.
When more than one request requires an exclusive lock against the same resource, VSAM queues the second and subsequent requests until the resource is freed and the lock can be granted. However, VSAM does not queue requests for resources locked by a retained lock (see Active and retained states for locks).