Oracle Database Administration: The Essential Refe

Redo Logs

Redo logs, also called online redo log files, are critical to Oracle’s ability to recover from a failure. Proper configuration of redo logs is critical not only to overall database performance, but also to your ability to recover the database (see Chapter 4). Guidelines include the following:

• Use Oracle’s built-in mirroring capability and put multiple sets of redo log files on different disk devices.

• Allocate enough redo log files so that Oracle does not have to wait for a file to complete archiving before it is reused. Oracle requires at least two redo log files, but four or more may be necessary.

• Allocate redo log files that are large enough to prevent too many log switches, but small enough to support good recovery if the current online log file is lost in a failure. With smaller files, you will probably be able to recover all transactions that have been archived, whereas a large log file size exposes the database to the potential for more lost transactions.

• Set the INIT.ORA parameter LOG_CHECKPOINT_INTERVAL to a value larger than the size of your redo log files. This will prevent checkpoints until the log file is full (which forces a checkpoint). This parameter is expressed in database blocks.

Warning

Remember that a log switch causes dirty (i.e., updated) buffers to be written to disk from the SGA.

• If you are running Oracle7, consider setting the INIT.ORA parameter CHECKPOINT_PROCESS to TRUE. Doing so creates a separate process that performs the checkpoint, rather than the ...