Specifying enqueue and dequeue requirements

Protecting database integrity when the same database record is concurrently updated requires you to estimate the number of events to be stored (enqueued) and released (dequeued) in internal storage.

The online IMS system protects the integrity of the database when concurrently running programs are updating the same database record. A record of the inter-level update events is maintained for program isolation in tables defined in the control program storage. These are termed enqueue/dequeue tables and consist of 24-byte entries in a z/OS® system. As programs reach synchronization points, the entries are freed and the storage can be reused. You need to estimate the number of events that might be recorded for concurrent execution of programs that might process against the same segment type.

The storage is allocated above the 16 MB line.