db_block_buffers = 360448 db_block_lru_latches = 4 db_block_size = 8192 _db_block_hash_buckets = 720896
Ok, what I have so far is: - using itrprof, I saw that 35% of my elapsed time was based on waits of "cache buffers chains" latches. - checking v$latch_children (latch#=66), there are a good number (8-10 I'd guess) of the 4096 children that have a very high (10k+) number of sleeps - the rest of the children (of this type latch) have sleep counts are 10-12, so we have a ton of contention on a low # of "cache buffers chains" latches. - joining with x$bh (v$latch_children.addr=x$bh.hladdr), I see that the most contentioned-for of these latches (51,240 sleeps!) has 66 blocks on the chain. Checking with all_objects, I'm noticing that these blocks are scattered in some of the more important (and most-accessed) tables and indexes - The other latch children that have high sleep counts also have 30-50 buffers in their chains Questions: - to me, 66 seems awfully high - is it? - the sleep count is obviously high from what I can tell - is it definitely tied to the buffer chain this latch is protecting being so long and just happening to be 66 buffers that are mostly important tables and indexes? - I haven't set it by hand, but _db_block_hash_buckets = 720896 and this is 11 * 2^16. Everything I've read says it should be a prime number (and that jives with my comp sci background) - why is it not prime, why is it exactly twice db_block_buffers? - the number of children for "cache buffers chains" is 4096. Now, increasing that could have a positive effect on distributing the contention, but since the sleps are so heavily skewed to only a few of the children as it stands, I don't get the feeling that's the right fix. Anyone have any advice to offer? Pages/URL's that can help give some advice? It's worth noting that these latches are basically non-existant as wait events at low load - "log file sync" is about the only wait event I see at low loads, and I'm working on reducing my commit counts much further to help tackle that. Thanks!! 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).
