Release Notes

5.24 Potential Problem When Restoring Files

Problem: When different versions of the same file are linked to a database at different times, the Data Links File Manager (DLFM) Retrieve daemon does not retrieve the correct version of the file from an archive when the database gets restored.

Background: When a database is restored from a backup image, the files that were linked in that backup image also get restored in the Data Links Manager file system (DLFS) from the archive. Here is how the DB2 Data Links Manager retrieve-and-restore process works.

• If the last modification time and size attributes of the current version of a file on disk are different from the attributes of the file to be restored from the archive, then the current file on disk is treated as a different version of the file. The current file on disk gets saved as filename.MOD, and the original version of the file from the DLFM archive gets restored. For example, if the current file name is abc, then abc gets copied to abc.MOD.
• If the last modification time and size attributes of the current file on disk are the same as those of the file to be restored from the archive, then the Data Links Retrieve daemon assumes that the file has not been modified, and it will not restore the version of the file from the archive.

Important: It is possible to modify a file but not have the last modification time and size attributes change. Such "hidden modifications" are done by making a change that does not affect the file size, and then resetting the last modification time attribute to that of the original file.

Example: Suppose you have a database called DBTEST, and it contains a table with a DATALINK column. You then perform the following tasks, in the order listed:

1. Create a file called fileA in a DLFS-mounted volume. This is the first version of the file.
2. Insert the fileA reference (a URL) into the DBTEST database.
3. Take a backup of the DBTEST database.
4. Delete the fileA reference from the DBTEST database.
5. Delete fileA from the DLFS-mounted volume.
6. Create another file named fileA in the DLFS-mounted volume. This is the second version of the file.
7. Insert the fileA reference (a URL) into the DBTEST database.
8. Restore the DBTEST database from the backup image.

The DLFM Retrieve Daemon copies the second version of fileA to fileA.MOD, then copies the first version of fileA from the archive onto the DLFS-mounted volume as the working version of fileA.

However, if both versions of fileA have the same last modification time and size attributes, the DLFM Retrieve Daemon does nothing, because it assumes that the files are actually the same version.

The result is that the second version of the file -- rather than the first version -- remains on the DLFS-mounted volume. You have not truly restored the file system to the same state it was at the time of the backup.

Solution: Ensure that your application does not replace a file with a newer version of that file with the same attributes (last modification time and size).