I got to see over 1,000 on a couple of cache buffers chains at one Oracle7 site a few years ago. This was prior to when Server Technologies set the limit of CR blocks in the buffer cache to 42 (spooky), and then eventually created (I think) the _db_block_max_cr_dba parameter.
The cause was an application that used a "select for update / update / commit" on one-row/one-column tables to generate sequence numbers (instead of using real Oracle sequences). Cary Millsap Hotsos Enterprises, Ltd. http://www.hotsos.com Upcoming events: - 2003 Hotsos Symposium, Feb 9-12 Dallas - RMOUG Training Days 2003, Mar 5-6 Denver - Hotsos Clinic 101, Mar 26-28 London -----Original Message----- Lewis Sent: Thursday, January 23, 2003 1:50 PM To: Multiple recipients of list ORACLE-L You could try: select file#, dbablk, count(*) from x$bh group by file#, dbablk having count(*) > 5 ; (technically you should include the tablespace number, but that won't matter if you have less than 1022 files). This will report the blocks which have an unusually large number of CR copies in the buffer. There is a nominal limit of 7, but if your buffer is excessive for the work done then there is a fair chance that the most intensively used blocks will have far more buffers. (The worst case I saw was something like 75). The side effects of this would include lots of spinning and sleeping on the cache buffers chains latch. Regards Jonathan Lewis http://www.jlcomp.demon.co.uk Coming soon a new one-day tutorial: Cost Based Optimisation (see http://www.jlcomp.demon.co.uk/tutorial.html ) Next Seminar dates: (see http://www.jlcomp.demon.co.uk/seminar.html ) ____England______January 21/23 ____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]> Date: 23 January 2003 19:05 I've got a cust that is showing some signs that one would think is having a horrible problem on I/O... I suspect it is the "error" of having a **HUGE** value in db_block_buffers and it's constantly crunching memory trying to figure out which ones to free up. It's only 256 meg, but depending on load, it may be too much. SGA is 687 meg. While I've got hundreds of SQL, I'm not sure I have one to diagnose buffer utilization. It's also version 8.1.7 and I could probably do some tweaking of buffers. It's Oracle CRM with a lot of customization and I'm also finding some SQL that's getting a bit ugly under there. Maks. -- 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). -- Please see the official ORACLE-L FAQ: http://www.orafaq.net -- Author: Cary Millsap 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).
