RE: Mirroring redo log groups or not ?

  • From: "Crisler, Jon" <Jon.Crisler@xxxxxxx>
  • To: "Rich" <richa03@xxxxxxxxx>, <cicciuxdba@xxxxxxxxx>
  • Date: Wed, 8 Apr 2009 00:35:54 -0400

Its one of the top issues measured in AWR / ADDM.  The problem
corresponds to poor response time for disk as measured at the host, and
at the SAN level.



From: Rich [mailto:richa03@xxxxxxxxx] 
Sent: Wednesday, April 08, 2009 12:33 AM
To: cicciuxdba@xxxxxxxxx
Cc: mwf@xxxxxxxx; kennaim@xxxxxxxxx; david.barbour1@xxxxxxxxx; Crisler,
Jon; Rajeev Prabhakar; Oracle-L Freelists
Subject: Re: Mirroring redo log groups or not ?


Back to the OP's question.

I think you mean "log file sync", right?

This means a session waits for LGWR to write redo to disk after commit
or rollback.
It is usually due to too many commits or short transactions; you should
commit in batch or use faster redo log disk IO.

However, we need more information.  This wait has numerous steps with
even more implications.

First off, what makes you think this is THE issue?

What are the following:
"redo write time" statistic
"log file parallel write" waits

Is the system otherwise busy during high numbers of this event?

It may not be as simple as just moving the redo logs to faster disks...

Other related posts: