$)CFrom my R11 11.0.3 system : (11.0.3 against 8.1.7.2.1 on Tru64, 4CPUs, db_block_lru_latches=16)
MIN(BUFFERS_PER) MAX(BUFFERS_PER) AVG(BUFFERS_PER) SUM(BUFFERS_PER) ---------------- ---------------- ---------------- ---------------- 69 119 93.8242188 96076 Do I have a problem ? Very long buffer-chains, huh ! Nobody's complaining about performance. CPU util is generally 40% to 80% only occasssionally at 90%+ when there are more than 6 reports running concurrently. Can't remember why I set db_block_lru_latches to 16, back in June 2001 when the DB was 8.0.5 Hemant K Chitale Principal DBA Chartered Semiconductor Manufacturing Ltd [EMAIL PROTECTED] 01/03/2002 02:23 AM Sent by: [EMAIL PROTECTED] Please respond to ORACLE-L To: Multiple recipients of list ORACLE-L <[EMAIL PROTECTED]> cc: (bcc: CHITALE Hemant Krishnarao/IT/CHRT/ST Group) Subject: Re: Perf Advice Needed: cache buffers chains, high waits, _db_block_hash_buckets >From my biggest problem child. No bind variables, tends to get busy at times. Mission critical of course. MIN(BUFFERS_PER) MAX(BUFFERS_PER) AVG(BUFFERS_PER) SUM(BUFFERS_PER) ---------------- ---------------- ---------------- ---------------- 1 17 5.45231072 5545 1 row selected. >From our production SAP system: MIN(BUFFERS_PER) MAX(BUFFERS_PER) AVG(BUFFERS_PER) SUM(BUFFERS_PER) ---------------- ---------------- ---------------- ---------------- 1 13 4.05840759 41899 1 row selected. Jared James Manning <[EMAIL PROTECTED]> Sent by: [EMAIL PROTECTED] 02/28/02 09:13 AM Please respond to ORACLE-L To: Multiple recipients of list ORACLE-L <[EMAIL PROTECTED]> cc: Subject: Re: Perf Advice Needed: cache buffers chains, high waits, _db_block_hash_buckets [Mogens N)*rgaard] > Amen. Contention for cache buffers chains means too much logical IO, > ie. find and exterminate heavy SQL. I don't see why the heavy SQL would result in the chain having 66 buffer heads in it, though, or why the sleep count would be so skewed. And my core question is still whether the number of buckets being non-prime is "normal" or not - it seems awfully wrong to me. That there's a lot of contention *is* a factor of the SQL, but the fact that it's so skewed to only a few chains is what worries me more. Once I have the contention down to a particular latch, but that latch protects a buffer chain with 66 buffer heads in it, how can I find out which ones of the 66 are generating the most attempts at that latch? Tell ya what - can I get a few ppl to run this query? It tells the min/max/avg for the number of buffers associated with each chain and if my numbers are high I can at least have a chance of spreading out the buffers over more chains (by upping the number of latches from 4k to 16k, 32, whatever) - it won't drop the actual IO any, of course, but since I don't have a hard fix on which buffers of the 66 are really the source of my contention, I'm not sure where to go from here. SELECT min(buffers_per), max(buffers_per), avg(buffers_per), sum(buffers_per) FROM ( SELECT count(*) buffers_per, hladdr FROM x$bh b, all_objects o, v$latch_children v WHERE b.HLADDR=v.addr AND b.obj=o.object_id AND v.name LIKE '%cache buffers %' GROUP BY hladdr ) My results: min = 39 max = 119 avg = 55.06 sum = 225555 If this shows to be about the same in other (well-tuned) Oracle DB's, then I won't worry as much about the number of buffers in each chain and would then focus on trying to isolate the specific buffers, then the source SQL causing the problem, etc. Given my previous sql trace analyses, I have a good idea what the problem SQL statement is, but it's a bit of a necessary evil right now (a join of a table (260k rows) and a materialized view (2k rows), 6 conditions in there where, and it gets executed a ton, probably on the order of 10x a second at peak) - all indexes that helped performance are created and around already. :( But, ideally I'd like to be able to prove this is the cause of the "hot buffers" before fixing anything. Thanks, guys!! James -- James Manning <[EMAIL PROTECTED]> GPG Key fingerprint = B913 2FBD 14A9 CE18 B2B7 9C8E A0BF B026 EEBB F6E4 -- Please see the official ORACLE-L FAQ: http://www.orafaq.com -- Author: James Manning INET: [EMAIL PROTECTED] 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: [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.com -- Author: INET: [EMAIL PROTECTED] 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: [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.com -- Author: INET: [EMAIL PROTECTED] 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: [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).