Re: High consistent gets , 10046

If you can check it in real time, you will probably find that you have a very large number of CR copies of the few blocks that are the focus of the concurrent activity.

The excess time is likely to be down to a mixture of CPU as Oracle trawls through the chain looking for the correct copy, and latch contention because of the time the latch has to be held whilst the correct copy is being found.

'select for update ...' seems to be particularly prone to this problem - especially if you have an over large db_cache_size, that allows for lots of blocks in state 'FREE'. (even a reasonably size buffer can produce this effect if there is a process elsewhere which is dropping or truncating objects on a regular basis).

You may be able to reduce the impact of the problem by spreading out the rows that need to be updated - e.g. by increasing the number of freelists, or hash partitioning the table. If this is a relatively small, static sized, table moving it to a single table hash cluster may help.

Regards

Jonathan Lewis
http://www.jlcomp.demon.co.uk

Now available One-day tutorials:
  Cost Based Optimisation
  Trouble-shooting and Tuning
  Indexing Strategies

(see http://www.jlcomp.demon.co.uk/tutorial.html )

____UK_______April 8th
____UK_______April 22nd

____Denmark May 21-23rd

____USA_(FL)_May 2nd

Next dates for the 3-day seminar:
(see http://www.jlcomp.demon.co.uk/seminar.html )

____UK_(Manchester)_May
____USA_(CA, TX)_August

The Co-operative Oracle Users' FAQ
http://www.jlcomp.demon.co.uk/faq/ind_faq.html

• Original Message ----- To: "Multiple recipients of list ORACLE-L" <ORACLE-L_at_fatcity.com> Sent: 13 March 2003 15:24

> Dear listers,
>
> I'm hunting for top LIO consumers to give a relief to our DB cpu and
found
> something that looks interesting.
>
> Many plain good queries show up way to high cr when executed in
concurrent
> environment (50 threads) while perform as predicted when executed
from
> SQL*PLUS.
>

-- 
Please see the official ORACLE-L FAQ: http://www.orafaq.net
-- 
Author: Jonathan Lewis
  INET: jonathan_at_jlcomp.demon.co.uk

Fat City Network Services    -- 858-538-5051 http://www.fatcity.com
San Diego, California        -- Mailing list and web hosting services
---------------------------------------------------------------------
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).