It may have changed in 9, but I'm pretty sure the
keep, recycle pools are not "identical" to the default
cache in terms of the hot/cold boundary. You could
always tweak the relevant underscore parms to make
them all the same - but you'd want to be very sure
that you could get maximal use out of them all of the
time.
Since the advent of IOT's I haven't seen much great
benefits in keep pools, but I do like recycle pools
mainly to avoid someone munching more buffer cache
with silly queries.
hth
connor
- becker.bill_at_marshfieldclinic.org wrote: >
> Hello,
>
> Env: 9.2.0.2 on Solaris 2.9
>
> We are currently considering a proposal regarding
> the use of the 3
> buffer pools represented by db_cache_size,
> db_keep_cache_size,
> and db_recycle_cache_size. I am wondering if this is
> a good idea
> or a bad idea. The proposal follows.
>
> >>
> The buffer pool space can be divided into 3 separate
> pools: db_cache_size, db_keep_cache_size, and
> db_recycle_cache_size.
> Despite the names, the blocks are all treated
> exactly the same with
> regard to the Least Recently Used (LRU) algorithm.
> The retention time
> of a database block in any of these pools is
> dependent upon the size
> of the pool, how often the block is referenced, and
> the probability
> of the block being displaced by a more popular
> block.
>
> The names Oracle has assigned to these pools reflect
> more of an intention
> than anything else; the keep pool is intended to be
> sized large enough
> to retain all frequently-referenced data; the
> recycle pool is intended to
> be sized small to recycle blocks not desired in
> memory, and the db_cache_size
> pool is intended for everything else.
>
> Funtionally, Oracle could have named these
> db_cache1, db_cache2 and db_cache3.
>
> Currently, we utilize just 1 cache, the
> db_cache_size. I am proposing that
> we utilize all 3 caches in some way; the rationale
> for this is that it is better to
> have 3 smaller caches of 800M, each managing 1000
> objects, than it is to have 1 large
> cache of 2.4G managing 3000 objects.
> >>
>
> The rest of this proposal suggests a method for
> distributing the various tables
> and indexes in our system to the 3 caches; it
> suggests a roughly equal division
> among the 3 caches based upon subject area and usage
> stats.
>
> 1) Is the information above accurate?
> 2) Is it better to have 3 smaller caches than 1
> large cache? (Assuming the objects
> are distributed among the caches about equally
> based upon usage stats)
>
> Thanks to those who read this far.
> More thanks to any responders.
> Most thanks to responders with helpful suggestions.
>
> --
> Please see the official ORACLE-L FAQ:
> http://www.orafaq.net
> --
> Author:
> INET: becker.bill_at_marshfieldclinic.org
>
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Received on Thu Feb 13 2003 - 04:33:56 CST
