Re: I/O EVENTS

Download the YAPP paper ;-)

Anjo.

John Kanagaraj wrote:

> Greg,
>
> > > Can I assume a i/o bottleneck from the following
> > >
> > > select * from v$system_event
> > > order by TIME_WAITED;
> >
> > No. Wait events may only make up a small amount of
> > processing that Oracle
> > is doing for you.
>
> Hmm.... I wouldn't think so. If there were just _one_ overall view that I
> could check to determine an Oracle bottleneck, it would be this view. A
> rollup of V$SESSION_WAIT is also effective in determining the _current_
> bottleneck.
>
> As to the original question: (And as with many other questions) It depends!
> The average_wait times displayed by V$SYSTEM_EVENT against specific events
> is a good indication of the 'bottleneck'. Just yesterday, I was debugging
> 'slow response' from a test database. The top wait events were for 'direct
> path read' and 'direct path write', with inordinate values for AV_WAIT (upto
> 932 CS or 9 secs!). This clearly pointed to some misconfigured Async I/O (It
> was on a Sun box where async_io default to TRUE). I then had the SA look at
> the Async config and it turns out that the Veritas layer was misconfigured -
> hopefully this has been sorted out. There have been numerous other examples
> - and I am not alone here - where DBAs have used V$SYSTEM_EVENT to determine
> the bottleneck. If I were 'S B', I would look at the avarage wait values for
> I/O and compare them to the manufacturer's claims. If they don't match or or
> not close, then it _may_ be an I/O bottleneck.
>
> I would recommend purchasing (or even stoop to the level of purloining a
> copy from a friend!) the most excellent 'Oracle Performance Tuning 101' book
> written by Gaja and Kirti from this list. This question is dealt in great
> detail therein, and I am sure they would be happy to answer any further
> queries.
>
> John Kanagaraj
> Oracle Applications DBA
> DBSoft Inc
> (W): 408-970-7002
>
> The manuals for Oracle are here: http://tahiti.oracle.com
> The manual for Life is here: http://www.gospelcom.net
>
> ** The opinions and statements above are entirely my own and not those of my
> employer or clients **
>
> --
> Please see the official ORACLE-L FAQ: http://www.orafaq.com
> --
> Author: John Kanagaraj
> INET: john.kanagaraj_at_hds.com
>
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-- 
Please see the official ORACLE-L FAQ: http://www.orafaq.com
-- 
Author: Anjo Kolk
  INET: anjo_at_oraperf.com

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