Re: log file sync event

  • From: "Alex Gorbachev" <gorbyx@xxxxxxxxx>
  • To: dubey.sandeep@xxxxxxxxx
  • Date: Thu, 8 Jun 2006 21:19:08 +0200

To reduce log file sync you need to reduce number and size of IOs per
physical device used for redo logs and remove all possible contention
(i.e. dedicate disks).

Reduce number and size of IOs per physical device:
- add more devices
- reduce frequency of commits
- check you log_buffer if it's not too smal and gets filled to 1/3 too
often - usually not the case with OLTP anyway.
- reduce amount of redo (don't update when not required - like columns
with the same values and rows that can be skipped).
- "do less work" on application - you would be surprised how much can
be saved and optimized there.
I would look on these points from bottom up.

Removing contention - are your backup destination/datafiles/archive
log destination sharing the same physical disks? If yes than your IO
subsystem gets more saturated. Consider optimizing your IO layout -
dedicating seprate disks to redo logs.

RMAN backup itself doesn't influence LGWR unlike online backup without RMAN.

2006/6/8, Sandeep Dubey <dubey.sandeep@xxxxxxxxx>:
I am using 10.2 on linux for OLTP system. I am getting log file sync
as top event. I can not change disk or combine transactions in one or
some thing other as suggested in metalink.

Does rman backup has any effect on this event as I see this event
going up during backup time and performance goes down the drain.

How can I reduce this wait event?



-- Best regards, Alex Gorbachev

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