IBM SC34-7012-01 manual Recoverable files

READ	WRITE
UPDATE

====== Locking =====

during update (See Note below)

Task A

SOT		READ		WRITE		SP
		UPDATE
			===Wait===	===== Locking ====
				during update
				(See caption
Task B				below)
	SOT				SP
Abbreviations:			Note:	For BDAM and VSAM
SOT:	Start of task			non-RLS, this locking
SP:	Syncpoint			grants exclusive control.

Figure 13. Locking during updates to nonrecoverable files. This figure illustrates two tasks updating the same record or control interval. Task A is given a lock on the record or control interval between the READ UPDATE and WRITE commands. During this period, task B waits.

READWRITE

UPDATE

The lock extends to the end of the UOW

===========================================

Task A

SOT

WRITE

READ UPDATE

Locked

===============Wait============== ====== until ===== end of UOW

Task B

	SOT	SP	SP
Abbreviations:
SOT:	Start of task
SP:	Syncpoint

Figure 14. Locking (enqueuing on a resource) during updates to recoverable files. This figure illustrates two tasks updating the same record or control interval. Task A is given an exclusive lock on the record until the update is committed (at the end of the UOW). During this period, task B waits.

Recoverable files

For VSAM or BDAM files designated as recoverable, the duration of the locking action is extended. For VSAM files, the extended locking is on the updated record only, not the whole control interval.

Chapter 13. Programming for recovery 155