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Home -> Community -> Mailing Lists -> Oracle-L -> RE: Question about buffer cache
John,
My earlier assumptions were wrong (usually are, that's why I test). I set up a 9.2 instance with these parameters:
db_cache_size=300M db_keep_cache_size=40M db_16k_cache_size=40M db_block_size=8192
Then, I created a tablespace MY16KTBSP with a 16k block size. Then, create table TESTA tablespace MY16KTBSP storage(buffer_cache KEEP); And this works. Does this really utilize the keep buffer cache? I'm not sure because it also worked in another test when I had no keep buffer. I'm not sure how to tell which buffer the blocks are in right now, maybe another list user can help us both with that. However, I just read your question again and realized I'm not anywhere in the neighborhood of addressing your issue which is your 'waits'. We aren't concerned with the number of waits (yes, but not only), but also the time spent waiting and why. A lot more information is needed really. Size and content of the table? Other indexes on the table? Are statisics up to date and accurate? Is use of this index really appropriate, sometimes full table scan is faster. Something else maybe another person could address, I'm not sure that db file sequential reads are physical only. They may be physical and logical depending on your blocks already being read into buffer. I'm thinking it doesn't matter so much which buffer, default, keep, or 16k is being used, if further analysis/testing shows benefit of this index being in cache, use keep. Test available scenarios a few times and use which is best.
>>> DLANDRUM_at_zalecorp.com 02/20/03 10:54AM >>> Hi John,
If I'm understanding what I'm reading from the 9i Concepts Guide, I think that non-default block size objects can only go into the cache with the same block size (meaning it can't go into keep buffer). I'm making this assumption because we can't create a tablespace of 16k blocksize until db_16k_cache exists. However, I'm working on testing this today and will reply with results.
Darrell
>>> JBaylis_at_mail.canfor.ca 02/19/03 01:50PM >>> I have indexes in a 16k page size tablespace. I have the following init.ora parameters:
db_block_size=4096 db_cache_size=600M db_keep_cache_size=200M db_16k_cache_size=200M
If I alter an index to put it in the keep pool, how does Oracle hande the discrepancy between the 4k default keep buffer and the 16k index block size?
Am I better off keeping the index in the 16k cache or in the db_keep_cache pool?
Since statspack shows:
Event Waits Timeouts Time (s) (ms)/txn
---------------------------- ------------ ---------- ---------- ------ -------- db file sequential read 2,725,553 0 40,710 15355.2
I assume my indexes should be cached more to reduce the waits. Is that correct?
Any advice would be appreciated.
Thanks
John Baylis
Database Administrator
Canadian Forest Products Ltd.
Vancouver B.C. Canada
> (604) 697-6476 (Office)
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-- Please see the official ORACLE-L FAQ: http://www.orafaq.net -- Author: Darrell Landrum INET: DLANDRUM_at_zalecorp.com 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). -- Please see the official ORACLE-L FAQ: http://www.orafaq.net -- Author: Darrell Landrum INET: DLANDRUM_at_zalecorp.com 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).Received on Thu Feb 20 2003 - 16:30:05 CST
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