Events in the recovery process

Db2 can recover a page set by using a backup copy.

The Db2 recovery log contains a record of all changes that were made to the page set. If the data needs to be recovered, Db2 restores the backup copy and applies the log changes to the page set from the point of the backup copy.

To recover a page set, the RECOVER utility typically uses these items:

  • A full image copy; which is a complete copy of the page set.
  • For table spaces only, any later incremental image copies that summarizes all changes that were made to the table space since the time that the previous image copy was made.
  • All log records for the page set that were created since the most recent image copy.

The following figure shows an overview of a recovery process that includes one complete cycle of image copies.

Figure 1. Overview of Db2 recovery
Begin figure description. The recovery events occur in the following order: log start, full image copy, incremental image copy 1, and incremental image copy 2. End figure description.

The SYSIBM.SYSCOPY catalog table can record many complete cycles. The RECOVER utility uses information in the SYSIBM.SYSCOPY catalog table for the following purposes:

  • To restore the page set with data in the most recent full image copy
  • For table spaces only, to apply all the changes that are summarized in any later incremental image copies
  • To apply all changes to the page set that are registered in the log, beginning with the most recent image copy

If the log was damaged or discarded, or if data was changed erroneously and then committed, you can recover to a particular point in time. This type of recovery limits the range of log records that the RECOVER utility is to apply.