Managing system logs

Recovering a shared database requires log data from each sharing IMS system. A DBRC GENJCL.RECOV command or a Database Recovery utility execution using DBRC will fail if logs need to be merged for the database.

You can use the merge function of the IMS Database Change Accumulation utility (DFSUCUM0) to merge the log data from all sharing IMS systems.

You can run the Database Change Accumulation utility (DFSUCUM0) as often as your workload requires without first establishing a complete set of log volumes. Doing so allows you to accumulate change records on a timely basis, keeping the log input to a reasonable number of volumes, without taking databases offline or bringing down IMS. Doing so can, however, increase the size of the change accumulation data set.

IMS stores records from these partial subsets of log volumes on the change accumulation data set as spill records. These records retain their individual update characteristics.

Before running the Database Recovery utility (DFSURDB0), you must run the Database Change Accumulation utility, specifying a complete set of log volumes for the DBDS that you need to recover. If you run the Database Change Accumulation utility with an incomplete set of logs, specify the change accumulation output data set as input to your next Database Change Accumulation run. If a change accumulation data set represents an incomplete set of logs for the DBDS that you need to recover, the data set is not valid for recovery of that DBDS.

The DBRC LIST.CAGRP command displays whether the set of log volumes for each DBDS of the change accumulation group is complete or incomplete.

You can run DFSUCUM0 with a valid set of log volumes at any time in order to minimize the size of the change accumulation data set. To establish a valid set of logs in a data-sharing complex, use the following procedure:

  1. Suspending operation of all batch IMS systems
  2. Using the /DBRECOVERY DB or UPDATE DB STOP(ACCESS) command to terminate database access for all but one online IMS system
  3. Forcing a log switch on the remaining online IMS system