VSAM maintains a single central lock structure using the MVS™ coupling facility. This central lock structure provides sysplex-wide locking at a record-level. The lock is used to control updates, for CR and CRE reads, and to serialize adds to an ESDS data set when used for DFSMStvs processing.

For CICS®, the lock owner name is the application identifier (APPLID) of the CICS region, plus the unit of work ID. For DFSMStvs, the lock owner name is based on the DFSMStvs instance name combined with the 16-byte URID supplied by RRS.

There is no need for an application that is using DFSMStvs services to provide the URID when invoking VSAM. When VSAM invokes DFSMStvs services, DFSMStvs determines the URID by using the RRS unit of recovery under which the VSAM request was issued. VSAM builds the lock name using the unit of work identifier (UOW ID) or URID, the record key, and the name of the CICS APPLID or DFSMStvs instance.

If a request is made to update a recoverable data set, the associated exclusive lock must remain held until the next sync point. This ensures that the resource remains protected until a decision is made to commit or back out the request. If DFSMStvs fails, VSAM continues to hold the lock until DFSMStvs restarts.