RE: I/O EVENTS

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

Fat City Network Services    -- (858) 538-5051  FAX: (858) 538-5051
San Diego, California        -- Public Internet access / Mailing Lists
--------------------------------------------------------------------
To REMOVE yourself from this mailing list, send an E-Mail message
to: ListGuru_at_fatcity.com (note EXACT spelling of 'ListGuru') and in
the message BODY, include a line containing: UNSUB ORACLE-L
(or the name of mailing list you want to be removed from).  You may
also send the HELP command for other information (like subscribing).