Fw: direct IO

From: <Laimutis.Nedzinskas_at_seb.lt>
Date: Mon, 29 Nov 2010 07:36:43 +0200
Message-ID: <OFA339AAA7.EFB2F7B6-ONC22577EA.001EC7A1-C22577EA.001ED3AB_at_seb.lt>


>I believe that you would need to increase the buffer cache size to compensate OS file cache vanished by direct I/O.

true but as I said we do have full scans:

       > 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

The last thing I would like to play with are oracle hidden parameters ( I'am too old for that :)))) )


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I believe that you would need to increase the buffer cache size to compensate OS file cache vanished by direct I/O.



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2010/11/28 Mohammad Rafiq <rafiq9857_at_hotmail.com>
      You did not mention oracle version. Try to get it set aio-max-nr to
      1048576 (default is 65536). If it is 10.2.0.5 then it must be 1048576
      as a áwork around.

      Regards
      Rafiq

      > From: jcmiranda_at_oesia.com

      > To: przemolicc_at_poczta.fm; oracle-l_at_freelists.org
      > Date: Fri, 26 Nov 2010 12:58:22 +0100
      > Subject: RE: direct IO

      >
      >
      > 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/ > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > ---------------------------------------------------------------------- > Najlepsza wyszukiwarka tanich lot├│w! > Sprawd┼╝ >>> http://linkint.pl/f284a > > -- > http://www.freelists.org/webpage/oracle-l-- > http://www.freelists.org/webpage/oracle-l > >
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Received on Sun Nov 28 2010 - 23:36:43 CST

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