Sync points

Sync point processing finalizes changes to resources. Sync point requests specify actions to take place for the resource changed (for example, commit or abort). A sync point is when IMS DB actually processes the request.

Each sync point is based on a unit of recovery (UOR). A UOR covers the time during which database resources are allocated and can be updated until a request is received to commit or abort any changes. Normally, the UOR starts with a CCTL SCHED (schedule a PSB) request or an ODBA APSB call and ends with a sync point request. Other DRA thread requests can also define the start and end of a UOR.

A CCTL UOR is identified by a recovery token (PAPLRTOK) that is received as part of a thread request that creates a new UOR. It is 16 bytes in length. The first 8 bytes contain the CCTL identification. This identification is the same as the CCTL ID that was a final DRA startup parameter determined from USERID or PAPLUSID in INIT request. The second 8 bytes must be a unique identifier specified by the CCTL for each UOR.

Related Reading: See the request descriptions under CCTL-initiated DRA function requests for more information on the DRA thread requests.

IMS DB expects the CCTL or the ODBA application to make the sync point decision and the resulting request. In the case of a CCTL, the CCTL is the sync point manager and coordinates the sync point process with all of the database resource managers (including those other than IMS DB) that are associated with a UOR. In the case of an ODBA application, z/OS® Resource Recovery Services is the sync point manager and coordinates all the resource managers (including those other than IMS) that are associated with the UOR.

A CCTL working with a single resource manager may request a sync point in a single request or can use the two-phase sync point protocol which is required for a CCTL working with multiple resource managers. The single-phase sync point request can be issued when the CCTL has decided to commit the UOR, and when IMS DB owns all of the resources modified by the UOR.

An ODBA application must use the two-phase sync point protocol for committing changes to the IMS database.