Re: os cache vs. db cache
- From: "K Gopalakrishnan" <kaygopal@xxxxxxxxx>
- To: Brandon.Allen@xxxxxxxxxxx
- Date: Tue, 10 Jul 2007 11:31:39 -0700
Alan,
I beg to differ here. Caching tables work excellently on paper. But
when you put that in to practice it will be otherwise. In real life,
they will not cached in the buffer cache and also they are subject to
the normal LRU or touchcount aging. There is a _small_table_threshold
defines the tables which are eligible for caching and/or when the
table is bigger than 2% of the buffer cache they will not be cached.
So the point here is, for the OP, with the 200-300M tables will NOT be
cached in the buffer cache unless he sets the db_cache_size (buffer
cache) 10-15G.
On 7/10/07, Allen, Brandon <Brandon.Allen@xxxxxxxxxxx> wrote:
I think you'd still be better off to cache those full table scans in the
Oracle cache (e.g. alter table my_fts_tab cache). That way, you avoid
having to copy them from the OS cache to the DB cache and all the
overhead that is involved with performing a consistent get, which would
make your performance even better.
For more info:
http://download.oracle.com/docs/cd/B19306_01/server.102/b14200/statement
s_7002.htm#i2215507
-----Original Message-----
From: Chris Dunscombe [mailto:chris@xxxxxxxxxxxxxxxxxxxxx]
One situation I've experienced was a smallish (< 250GB) third-party
online operational database on Solaris where the OS cache acted as a
cache for Full Table scans of tables around the 100-300 MB size. This
worked well although it was more by accident than design.
--
Best Regards,
K Gopalakrishnan
Co-Author: Oracle Wait Interface, Oracle Press 2004
http://www.amazon.com/exec/obidos/tg/detail/-/007222729X/
Author: Oracle Database 10g RAC Handbook, Oracle Press 2006
http://www.amazon.com/gp/product/007146509X/
--
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