Both the Connect CDC (SQData) IMS Log Reader and TM Exit automatically capture all database activity logged by online and BMP processing. Unit-of-work integrity is coordinated by IMS and CDCzLog for online message regions (MPRs), Fast Path regions and batch message processes (BMPs), as follows:
- When the IMS online transaction or BMP issues a SYNC or Checkpoint, the captured IMS data is also committed to a System LogStream.
- When the IMS online transaction or BMP fails or issues a Rollback (ROLB) command, the captured data in the CDCzLog is rolled back for that unit of work.
Certain z/OS IMS configurations can introduce conditions where two updates to the same Segment can be replicated out of sequence. The Apply and Replicator Engines can mitigate those corner cases using the SmartApply feature. The following sections describe how this condition can be introduced by either IMS Capture method.