Running epoch_watchdog

The epoch_watchdog script checks whether a replica’s epoch numbers have rolled back without a restorereplica command being run.

If a replica is restored improperly from backup, divergence can occur in the VOB family. When you restore a replica from backup, its epoch row is rolled back. If you do not run the restorereplica command on the replica before resuming development in the replica, divergence can occur.

For example, operations 1-700 are created in a replica and exported to sibling replicas. The replica is then restored from backup and its epoch number becomes 600 (operations 601-700 occurred after the backup copy was created). If the administrator does not run the restorereplica command, development resumes and new operations are recorded in the oplog starting with ID 601. These operations have the same ID as the operations that were exported to other replicas before the restoration, but the operations themselves are different. The restored replica has diverged from the other replicas.

The epoch_watchdog checks for this condition. Run this script regularly as a scheduled job on all replica server hosts. For example, the following job runs epoch_watchdog every three hours for all replicas on the host:

Job.Begin
  Job.Id: 20
  Job.Name: "epoch_watchdog"
  Job.Description.Begin:
  Run epoch_watchdog for each replica on this host.
  Job.Description.End:
  Job.Schedule.Daily.Frequency: 1
  Job.Schedule.StartDate: 3-Sep-2001
  Job.Schedule.FirstStartTime: 20:00:00
  Job.Schedule.StartTimeRestartFrequency: 03:00:00
  Job.DeleteWhenCompleted: FALSE
  Job.Task: 105
  Job.Args: -all
  Job.NotifyInfo.OnEvents: JobEndOKWithMsgs,JobEndFail
  Job.NotifyInfo.Using: email
  Job.NotifyInfo.Recipients: ms_admin
Job.End

This job uses the MultiSite Epoch Watchdog task, which is defined as follows:

Linux® task:

Task.Begin
    Task.Id:       105
    Task.Name:     "MultiSite Epoch Watchdog"
    Task.Pathname: epoch_watchdog
Task.End

Windows® task:

Task.Begin
    Task.Id:       105
    Task.Name:     "MultiSite Epoch Watchdog"
    Task.Pathname: epoch_watchdog.bat
Task.End

For more information about creating tasks and scheduling jobs, see the schedule reference page in the VersionVault Command Reference and the scheduler information in the Help.