Re: Inconsistent file IO times on AWR report

In this case you're probably seeing the effect of both the OS  file caching
and the SAN caching.

Harel Safra
(Sent from my phone, excuse the terseness)

ב-04/05/2010, בשעה 23:17, Neil Kodner <nkodner@xxxxxxxxx> כתב/ה:

Solaris 9, veritas 3.5, hitachi san.  Mount points look like:

/u01 on /dev/vx/dsk/rootdg/u01
read/write/setuid/delaylog/largefiles/qio/ioerror=mwdisable/dev=3d40005 on
Thu Mar 18 23:25:59 2010
/u02 on /dev/vx/dsk/rootdg/u02
read/write/setuid/delaylog/largefiles/qio/ioerror=mwdisable/dev=3d40006 on
Thu Mar 18 23:26:04 2010
/u03 on /dev/vx/dsk/rootdg/u03
read/write/setuid/delaylog/largefiles/qio/ioerror=mwdisable/dev=3d40007 on
Thu Mar 18 23:26:09 2010

filesystemio_options = asynch

For what its worth, 32gb server, 12gb sga, 7gb pga aggregate target, we're
always maxed out on RAM and swap, and our iowait, during business hours,
hovers around 25-30%.

On Tue, May 4, 2010 at 2:46 PM, Harel Safra <harel.safra@xxxxxxxxx> wrote:

>  Even if you're using direct io it still could be caching at the storage
> level.
> What is your disk/lun configuration?
>
> Harel Safra
>
>
> On 04/05/2010 16:11, Stephens, Chris wrote:
>
>  Since blocks from the heaviest hit tablespace are more likely to be in
> the os-cache, that would account for Oracle thinking blocks read from that
> tablespace are faster.  I guess that assumes you aren’t using direct-io.
>
>
>
> Chris
>
>
>
> *From:* oracle-l-bounce@xxxxxxxxxxxxx [
> mailto:oracle-l-bounce@xxxxxxxxxxxxx 
> <oracle-l-bounce@xxxxxxxxxxxxx><oracle-l-bounce@xxxxxxxxxxxxx>]
> *On Behalf Of *Neil Kodner
> *Sent:* Tuesday, May 04, 2010 7:35 AM
> *To:* oracle-l-freelists; Neil Kodner
> *Subject:* Inconsistent file IO times on AWR report
>
>
>
> I'm trying to get to the bottom of some performance issues and one of the
> things that stumps me is that my AWR reports show wildly inconsistent read
> times for my tablespaces.  The heaviest-hit tablespace consistently shows an
> average read time of .59ms.  The others range from 13 to 25ms in avg read
> time.  I dont find anything obvious when comparing matviews_index and
> matviews_data to the rest of the tablespaces when looking in
> dba_tablespaces.
>
>
>
> Given that all of the tablespaces are on the same hardware device and mount
> points, I would expect the average read times to be somewhat similar across
> the board.  Is this an invalid assumption?
>
>
>
> The tablespace and file details from awr can be found at
> http://goo.gl/CTaO
>
>
>
> I'll update the document with additional information as requested.
>
>
>
> Thanks,
>
>
>
> Neil
>
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