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" <[EMAIL PROTECTED]> 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: [EMAIL PROTECTED] 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: [EMAIL PROTECTED] (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).
