Journal Files

The JADE database maintains details of updates to databases in a journal (or audit log) file, which is used to:

• Recover the database to a consistent state after a crash (crash or restart recovery)

• Undo the effects of failed or incomplete transactions (abort recovery)

A set of active, or online, journal files is maintained, as well as multiple offline (or archived) journal files. The active journal files record current database activity. As journal files become no longer required for abort recovery, they are released. When released, a journal is considered offline, and can then be moved to another location. For more details, see "Journal Switches and Journal Numbers" under "Transaction Journal Files", later in this chapter. JADE also supports the use of transaction journals to perform a roll-forward recovery. Roll-forward recovery takes advantage of the fact that transaction journals hold details of all changes that have been made to the database. You therefore do not necessarily need to undo changes but instead can reapply changes. See also "Implementing a Database Recovery Strategy", in Chapter 1 of the JADE Synchronized Database Service (SDS) Administration Guide.

JADE database recovery and the JADE Database utility journal dump and verify operations accept compressed journals as input. If an uncompressed journal is not found at the target location, a check for a compressed journal is performed. If a compressed journal is found, it is uncompressed for use as input to the operation. The temporary uncompressed file is removed when the operation completes.