RE: Mirroring redo log groups or not ?

From: Crisler, Jon <>
Date: Wed, 8 Apr 2009 00:35:54 -0400
Message-ID: <56211FD5795F8346A0719FEBC0DB0675041A7D3C_at_mds3aex08.USIEXCHANGE.COM>

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 [] Sent: Wednesday, April 08, 2009 12:33 AM To:
Cc:;;; 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...

Received on Tue Apr 07 2009 - 23:35:54 CDT

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