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Oracle Tips by Burleson

Resizing Redo Logs

The administrator’s guide states that each database should have at least three groups of redo logs with each group having at least two members each. In addition, Oracle recommends that all redo log group members be the same size.

If your redo log sizes are too small (or too large), they can be easily resized while the database is up and running. The steps to resize the redo logs are as follows:

• Determine how quickly the logs are switching by checking the database’s alert log or the v$log_history view.
   

• Create a dummy redo log group containing one member. The size of the redo log group member should be large enough to give you enough time to complete the alterations below. 15 to 30 minutes should be enough time.
   

• Use the ALTER SYSTEM SWITCH LOGFILE statement to make the dummy the active log group. Use the view v$log to determine which group is active. Keep switching and checking until the dummy group becomes active.
   

• Drop the first redo log group (ALTER DATABASE DROP LOGFILE….) and then recreate the redo log group (ALTER DATABASE ADD LOGFILE….). If you try to drop a group that has become active for whatever reason, rest assured that Oracle is smarter than you are in this case and will prohibit you from doing so.
   

• Repeat the previous step until all of the permanent redo log groups have been resized.
   

• Drop the dummy log group by executing the ALTER DATABASE DROP LOGFILE… statement.

All of the Oracle certification tests will have numerous questions on redo logs.  Test candidates should have a strong knowledge of redo and archived redo logs including:

• How the Oracle environment uses redo logs
   

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