RE: direct IO

From: Juan Cruz Miranda Vigo <jcmiranda_at_oesia.com>
Date: Fri, 26 Nov 2010 12:58:22 +0100
Message-ID: <5A25A252E6111747ADBF7904B67E9DCA0183539B838E_at_MAILSERVER2.itdeusto.local>


We are getting

WARNING:io_submit failed due to kernel limitations MAXAIO for process=128 pending aio=110
WARNING:asynch I/O kernel limits is set at AIO-MAX-NR=3145728 AIO-NR=77074
WARNING:Oracle process running out of OS kernel I/O resources (1)
WARNING:Oracle process running out of OS kernel I/O resources (1)
WARNING:Oracle process running out of OS kernel I/O resources (1)

on several systems with linux pppc64 and it seems there are no patch for this error on this platform. I can┤t tell if direct i/o is slower.

Anyone know how to solve this problem?



De: oracle-l-bounce_at_freelists.org [oracle-l-bounce_at_freelists.org] En nombre de przemolicc_at_poczta.fm [przemolicc_at_poczta.fm] Enviado el: viernes, 26 de noviembre de 2010 10:21 Para: oracle-l_at_freelists.org
Asunto: Re: direct IO

On Thu, Nov 25, 2010 at 05:32:02PM +0200, Laimutis.Nedzinskas_at_seb.lt wrote:
> Looking for experiences/advices of others regarding one issue with direct
> IO.
>
> Recently we switched to another data center and some databases reported
> increased IO time.
> After investigating we found that IO is slower on file systems (Veritas,
> Solaris 10) mounted with direct io options.
> AWR shows more time on scattered reads but for the same number of blocks
> too.
> We are going to switch of direct IO and test but for the time beeing I am
> wandering why direct IO is bad in our case.
>
> We've got seriously increased times for statistics gathering which does
> full scan naturally - we've found 2 full scan sqls on the same table
> clearly comming from dbms_stats package . Full scan is not cached by
> oracle. But file system cache can help in that particular case.

Do you have exactly the same storage configuration in both data centers ?

We found that _usually_ switching from buffered filesystem to direct IO won't help unless you increase also Oracle buffers (so Oracle uses memory which had been used previously for filesystem buffering). Also on Veritas/UFS I recommend to turn on direct IO in Oracle (FILESYSTEMIO_OPTIONS=SETALL) and not in Veritas (we don't set any mount options in /etc/vfstab for Veritas filesystems).

If you bought Veritas ODM - just use it.

Regards
Przemyslaw Bak (przemol)

--
http://przemol.blogspot.com/





























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Received on Fri Nov 26 2010 - 05:58:22 CST

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