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RE: High waits/Timeouts - log file parallel write

From: John Kanagaraj <john.kanagaraj_at_hds.com>
Date: Mon, 27 Feb 2006 17:31:06 -0800
Message-ID: <BEE6A332AA61424EAE305CF89D6F75C84BAFF1@USSCCEVS101.corp.hds.com>


Tom,

Are you having a lot of control file writes precipitated by a small redo log file as compared to the redo size/rate and a large number of datafiles? You should be able to check this from the number of datafiles and redo log file/rate and have a feeling for amount of checkpoint I/O by comparing V$SYSSTAT's 'physical writes non checkpoint' to 'physical writes'. The former should lag the latter by a a very small percentage....

Regards,
John Kanagaraj <><
DB Soft Inc
Phone: 408-970-7002 (W)  

Co-Author: Oracle Database 10g Insider Solutions http://www.amazon.com/exec/obidos/tg/detail/-/0672327910/  

-----Original Message-----
From: oracle-l-bounce_at_freelists.org
[mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Steve Adams Sent: Monday, February 27, 2006 4:56 PM
To: pele_00_2000_at_yahoo.com
Cc: oracle-l_at_freelists.org
Subject: Re: High waits/Timeouts - log file parallel write

Hi Tom,

The 'log file parallel write' waits affect LGWR only. They do not affect the performance of user processes directly (although they do impact somewhat on your 'log file sync' wait duration). The number of timeouts is influenced by your use of asynchronous I/O and by how often LGWR is posted by user processes. It is not a useful indicator of performance problems.

I think you should be more concerned about the 'control file parallel write' waits that are probably affecting user processes directly.

@   Regards,
@   Steve Adams
@   http://www.ixora.com.au/         - For DBAs
@   http://www.christianity.net.au/  - For all


TP wrote:
> Hello all,
>
> I seeing high Waits, Timeouts from one the problem instance.
>
> Top 5 Timed Events
> ~~~~~~~~~~~~~~~~~~
> % Total
> Event
> Waits Time (s) Ela Time
> --------------------------------------------
> ------------ ----------- --------
> CPU time
> 8 40.51
> control file parallel write
> 642 5 25.56
> db file sequential read
> 343 2 9.40
> log file parallel write
> 9,697 2 7.99
> log file sync
> 425 1 5.69
>

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Received on Mon Feb 27 2006 - 19:31:06 CST

Original text of this message

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