Procedure Definition Language Statements › Exclusive Control

Exclusive Control

Exclusive control is an enqueuing mechanism CA Datacom/DB provides to protect database records against the following:

• Destructive simultaneous update by two more different tasks.
• This is governed by primary exclusive control.
• Two tasks consecutively update the same record, followed by an abend and transaction backout by one of those tasks. Without exclusive control, the update by the unaffected task might be backed out without the task being aware of it.
• This control is provided by secondary exclusive control.

Exclusive control operates at the logical record level. If Task 1 attempts to read a record for update that is held under either primary or secondary exclusive control by Task 2, it waits until Task 2 releases control of the record. Task 1 cannot get update control of the record until one of the following occurs:

• Task 2 completes.
• Task 2 issues a CHECKPOINT, TRANSMIT or CICS SYNCPOINT command.
• Task 2 abends and transaction backout completes.

If Task 2 is a long running batch job that is updating many database records without issuing CHECKPOINT commands, all online tasks that access those same records for update wait. This can degrade online response time.