Oplog scrubbing

Oplog entries must be kept for a significant period of time. They are required when the replica generates update packets. Oplog entries also may be required to help other replicas recover from catastrophic failures. If no replica can supply these entries, the replica being restored must be re-created. Because of the need to use oplog entries during synchronization, your synchronization strategy determines how often oplogs can be scrubbed.

For more information, see Restoring a replica from backup.

By default, an oplog entry is never scrubbed. Do not change this setting until you establish the synchronization pattern in the family and verify that packets are being exported and imported successfully.

When it is safe to delete oplog entries for a replica:
  1. Coordinate with other administrators to decide how long you must keep oplog entries.

    Each replica must keep entries for as long as necessary to allow restorereplica operations to complete successfully. The frequency with which you scrub oplog entries depends on the following factors:

    • The pattern of synchronization among replicas in the family
    • How often the replicas are synchronized

      Frequency of synchronization refers both to how often updates are exported and how often they are imported at other replicas. Also, consider setting up a verification scheme to ensure that packets are processed successfully at other replicas before any oplog entries are scrubbed.

    • How often you back up the replicas

      For example, if a replica is backed up weekly at all sites and you want to be able to restore to the backup from two weeks ago, each replica must keep three weeks of oplog entries. If replicas synchronize weekly, you must assume that the weekly packet has not been sent to the other replica, and add another week. Finally, for extra security, add another month. The result is a scrubbing time of two months.

  2. Create a scrubber parameter file specific to your VOB by copying ccase-home-dir /config/vob/vob_scrubber_params (Linux™ and the UNIX™ system) or ccase-home-dir\config\vob\vob_scrubber_params (Windows™) to the VOB storage directory of the replica.
  3. Make this new file writable.
  4. Edit the oplog line in this file. For example, to keep oplog entries for two months (62 days): 
    oplog -keep 62
Attention: If a replica's oplog entries are scrubbed before they are included in an update packet, you cannot export update packets from the replica. This is a serious error and compromises the integrity of the entire family.