IBM SC34-7012-01 Synchronization points, Exec Cics Discard Connection Exec Cics Discard Terminal

When a lock is first acquired, it is an active lock. It remains an active lock until successful completion of the unit of work, when it is released, or is converted into a retained lock if the unit of work fails, or for a CICS or SMSVSAM failure:

vIf a unit of work fails, RLS VSAM or the CICS enqueue domain continues to hold the record locks that were owned by the failed unit of work for recoverable data sets, but converted into retained locks. Retaining locks ensures that data integrity for those records is maintained until the unit of work is completed.

vIf a CICS region fails, locks are converted into retained locks to ensure that data integrity is maintained while CICS is being restarted.

vIf an SMSVSAM server fails, locks are converted into retained locks (with the conversion being carried out by the other servers in the sysplex, or by the first server to restart if all servers have failed). This means that a UOW that held active RLS locks will hold retained RLS locks following the failure of an SMSVSAM server.

Converting active locks into retained locks not only protects data integrity. It also ensures that new requests for locks owned by the failed unit of work do not wait, but instead are rejected with the LOCKED response.

Synchronization points

The end of a UOW is indicated to CICS by a synchronization point, usually abbreviated to syncpoint.

A syncpoint arises in the following ways:

vImplicitly at the end of a transaction as a result of an EXEC CICS RETURN command at the highest logical level. This means that a UOW cannot span tasks.

vExplicitly by EXEC CICS SYNCPOINT commands issued by an application program at appropriate points in the transaction.

vImplicitly through a DL/I program specification block (PSB) termination (TERM) call or command. This means that only one DL/I PSB can be scheduled within a UOW.

Note that an explicit EXEC CICS SYNCPOINT command, or an implicit syncpoint at the end of a task, implies a DL/I PSB termination call.

vImplicitly through one of the following CICS commands:

–EXEC CICS CREATE TERMINAL

–EXEC CICS CREATE CONNECTION COMPLETE

–EXEC CICS DISCARD CONNECTION

–EXEC CICS DISCARD TERMINAL

vImplicitly by a program called by a distributed program link (DPL) command if the SYNCONRETURN option is specified. When the DPL program terminates with an EXEC CICS RETURN command, the CICS mirror transaction takes a syncpoint.

It follows from this that a unit of work starts:

vAt the beginning of a transaction

vWhenever an explicit syncpoint is issued and the transaction does not end

vWhenever a DL/I PSB termination call causes an implicit syncpoint and the transaction does not end

vWhenever one of the following CICS commands causes an implicit syncpoint and the transaction does not end:

– EXEC CICS CREATE TERMINAL

Chapter 2. Resource recovery in CICS 15