Progress Fathom Replication
User’s Guide
Manually applying After Image extents
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 most recent blocks did not reach the target. For example, a TCP/IP failure could lose packets that were waiting for 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 only do so under the following conditions:
- The
transition
property (under the[server]
directive in the properties file) must be set tomanual
.- 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.
To apply AI extents:
- Display failure recovery information using the following command:
- 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 shows an example of the relevant section of the command output:
Determine the file number of the last applied AI extent. In this example the last applied extent is
3
. Since the value afterCompletely Applied to Target
isNo
, you will use3
as theextent_file_number
in Step 3.Since the value after
Completely Applied to Target
isYes
, you would use4
as theextent_file_number
in Step 3, since extent3
is already completely applied.- Use the appropriate AI extent file number in the following command:
As the command executes, it performs the following validation:
- The extent must exist and must be valid.
- The status of the extent must be
FULL
,BUSY
, orLOCKED
.- 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).
After you apply the AI extent, you can begin a manual transition of the target. For more information, see the "Manual transition" section.
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