Redo Log Files
Redo log files contain a ???recording??? of the changes made to the database as a result
of transactions and internal Oracle activities. Since Oracle usually caches changed
blocks in memory, when instance failure occurs, some changed blocks might not
have been written out to the datafiles. The recording of the changes in the redo logs
can be used to play back the changes lost when the failure occurred, thus protecting
transactional consistency.
These files are sometimes confused with rollback buffers supporting
concurrency and described in Chapter 8. They are not the same!
In addition, redo log files are used for ???undo??? operations when a ROLLBACK statement
is issued. Uncommitted changes to the database are rolled back to the database
image at the last commit.
Suppressing Redo Logging
By default, Oracle logs all changes made to the database. The generation of redo logs
adds a certain amount of overhead. You can suppress redo log generation to speed up
specific operations, but doing so means the operation in question won??™t be logged in
the redo logs and youwill not be able to recover that operation in the event of a failure.
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