During normal conditions, the target database is automatically updated with data from the source database. The updates are transmitted as blocks of data from the source's AI transaction log. After a failure condition, it is possible that the most recent blocks were unable to reach the target. For example, a TCP/IP failure could lose packets that were awaiting transmission.

You can recover the missing data by manually applying the after-image extents that contain the data that has not already been applied to the target. However, you can do so only under the following conditions:

  • The transition property (under the [server] section in the properties file) must be set to manual.
  • The agent must be in a pre-transition state.
  • The storage device that contains the source database AI extents must be accessible by the target machine. You cannot save AI extents on the same system where the source is running because the extents would not be accessible after a system crash. Network area storage (NAS) or storage area network (SAN) devices are ideal for storing AI extents.
  • If Replication AI streaming, the ai-streaming property under the [agent] section in the properties file, is enabled, the RSB cache must be empty before applying extents. If it is not empty, attempting to apply an extent, results in the following message:
    The extent cannot be applied. There are %d unapplied blocks remaining in the RSB
 cache. (19292)
    Note: While the replication agent main thread is in the applying-extent state, you cannot run the triggertranistion command. With AI Streaming replication, you cannot run subsequent applyextent commands while the agent is in the applying-extent state. The writer thread must first empty the RSB cache and the main agent thread will move out of the applying-extent state.

To apply AI extents:

  1. Display failure recovery information.

    Use the following command:

    dsrutil target-db-name -C recovery agent
  2. Determine the AI extent number from the command output. Select the last-applied AI extent or, if the last-applied extent was completely processed, select the next available extent.

    The following is an example of the relevant section of the command output:

                                  .
                              .
                              .
  Last AI Extent processed
   AIMAGE BEGIN date:              Tue Oct 18 13:33:31 2005
   AIMAGE NEW date:                Tue Oct 18 13:48:55 2005
   After Image File Number:        3
   File Last Opened:               Tue Oct 18 13:48:55 2005
   Completely Applied to Target:   No

    Determine the file number of the last-applied AI extent. In this example the last-applied extent is 3. Since the value after Completely Applied to Target is No, you will use 3 as the extent-name in the next step.

    If the value after Completely Applied to Target was Yes, you would use 4 as the extent-name in the next step, since extent 3 would have already been completely applied.

    Note: The After Image File Number corresponds to the Seqno that appears in the extent list when you use the applyextent qualifier with DSRUTIL. For more information, see DSRUTIL applyextent qualifier.
  3. Use the appropriate AI extent file number in the following command: 
    dsrutil target-db-name -C applyextent qualified-extent-name

    As the command executes, it performs the following validation:

    • The extent must exist and be valid.
    • The status of the extent must be FULL, BUSY, or LOCKED.
    • The AI extent file number either must be the same as the AI extent file number for the last AI block processed by the agent, or it must be the next extent file number (if the previous AI extent was completely processed).

    If the source database after-image extents cannot be applied to the target database before transition, the target database will not contain any of the unapplied source database transactions. In this case, unless the transactions can be recreated and re-entered after transition, you will lose an indeterminate number of transactions.

    After you apply the AI extent, you can begin a manual transition of the target. For more information, see Set up manual transition.