IBM SC34-7012-01 - Manual (Page 167)

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.
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.
READ WRITE
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.
Chapter 13. Programming for recovery 155