Saturday, October 10, 2009

Redo Log Files Sizing 10g

Redo Log Files Sizing
The size of the redo log files can influence performance, because the behavior of the
database writer and archiver processes depend on the redo log sizes. Generally, larger redo log files provide better performance. Undersized log files increase checkpoint activity and reduce performance.

Although the size of the redo log files does not affect LGWR performance, it can affect DBWR and checkpoint behavior. Checkpoint frequency is affected by several factors,including log file size and the setting of the FAST_START_MTTR_TARGET initialization parameter. If the FAST_START_MTTR_TARGET parameter is set to limit the instance recovery time, Oracle automatically tries to checkpoint as frequently as necessary.Under this condition, the size of the log files should be large enough to avoidadditional checkpointing due to under sized log files. The optimal size can be obtained by querying the OPTIMAL_LOGFILE_SIZE column from the V$INSTANCE_RECOVERY view. You can also obtain sizing advice on the Redo Log Groups page of
Oracle Enterprise Manager Database Control.

It may not always be possible to provide a specific size recommendation for redo log
files, but redo log files in the range of a hundred megabytes to a few gigabytes are
considered reasonable. Size your online redo log files according to the amount of redo your system generates. A rough guide is to switch logs at most once every twenty

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