What happens in the condense phase of an archive journal?

Document ID : KB000020292
Last Modified Date : 14/02/2018
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Description:

The archive journal utility consists of a few steps one of which is the condense. This document describes what occurs in that step.

Solution:

This is an outline of the ARCHIVE JOURNAL utility's condense phase. For any transaction that is still active, we may need to recover that transaction in the future, if it abends. So, all journal images for any transactions that are still active will need to stay on that disk journal file.

During the OFFLOAD phase, all images for all transactions on the disk journal are copied to the ARCHIVE. Images for completed transactions are removed from the disk journal. Images for transactions that were still active at the time of the offload are 'condensed', or moved up to the front of the journal segment. Only the BFOR images for the active transactions are saved in the condensed segment in case that transaction needs to be rolled back. The disk journal then has a condensed segment on it. You can see this if you issue the command:

DCMT DISPLAY JOURNAL

This command will show all disk journal files, and all segments on those files. Some files you may notice have more than one segment. The older numbered segments are the condensed segments that were processed by the ARCHIVE JOURNAL utility. These condensed segments will ultimately be removed from the journal when a subsequent ARCHIVE JOURNAL utility determines that those images are no longer required for automatic recovery, because their transactions have completed or were abended and rolled out.