BWO and the recovery point time

To recover a VSAM sphere, CICS® VR must have the following information.

Each data set after-image record on the log is associated with a file name but many files might be associated with the same data set. When a file is opened, the association between the file and the data set is recorded on the log by a tie-up record (TUR). For backups made without the backup-while-open facility, CICS VR uses this TUR to apply the log records to the correct data sets.

For backups made using the backup-while-open facility, CICS VR need not process a log from file-open time. Here, TURs for all open files are regularly written on the log during activity-keypoint processing. To reduce the number of TURs if the activity keypoint frequency is high, CICS ensures that there is at least a 30-minute separation between sets of TURs on the log. The recovery point is a time that can be converted to a position on a forward-recovery log. It is also the point when CICS VR forward recovery starts for VSAM data sets eligible for backup-while-open processing. Recovery of the data set requires only the records that are written after that position. Thus, CICS VR can ignore all previous records.

The recovery point is stored in the ICF catalog. It is set when the first file is opened for update against the data set, and it is updated during activity-keypoint processing and when the file is closed.

The recovery point is not the time of the current keypoint, because there might still be some uncommitted log records that have not been forced. Instead, it is the time of the start of the last keypoint that wrote a complete set of TURs and that completed earlier than the oldest uncommitted write to a forward-recovery log.

Note:
  1. Only one new recovery point is calculated during an activity keypoint. It is used for all data sets that are open for update and eligible for backup-while-open processing. A long-running task that updates a data set that uses the backup-while-open facility affects the forward recovery that is needed for all data sets.
  2. If you disable activity keypointing in your system; by specifying AKPFREQ=0 in your SIT, backup-while-open support is seriously affected because no more TURs are written and the recovery point is not updated after backup-while-open. Forward recovery of a data set that is eligible for backup-while-open processing must occur from the time that the data set was first opened for update.

CICS VR extracts the recovery point time of the restored backup from the RCDS or ICF catalog. It is not necessary or recommended to specify a STARTTIME keyword in your recovery run.


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Timestamp icon Last updated: Friday, 29 November 2013


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