Re: Where best to cache the disk

In article <783604402snz_at_sambusys.demon.co.uk> psb_at_sambusys.demon.co.uk writes:
>We are not using raw partitions for our tablespaces.
>Are we better off caching inside Oracle by using a large SGA
>and a small Unix disk cache or should we use a small SGA and
>a large Unix disk cache?
>
>I am tempted to assign all our spare memory to the Unix disk
>cache (by increasing NBUF etc) and to keep the SGA just big
>enough for DC_* dictionary caching.
>
>What say you?
>
>--
>Paul Beardsell SAM Business Systems Ltd
>~~~~~~~~~~~~~~ 21 Finn House, Bevenden St,
>pbeardsell_at_cix.compulink.co.uk London, N1-6BN, UK.
>psb_at_sambusys.demon.co.uk (+44 or 0)71 608-2391

I have increasingly been reading more information on papers suggesting that making the SGA the "main" buffer cache for Oracle data is way to go.

It seems logical to do this, although we don't have benchmark numbers to substantiate this information. But when you think abount it, if your main application is Oracle DBMS, then why not make your db_block_buffers as large as possible and reduce the UNIX buffer cache to a minimum value.

This it seems is ideal in a mostly read only application where queries are the order of the day. Although if your application is write intensive, then I don' think increasing your UNIX or Oracle caches will help much. I have read that Oracle writes are "sync'ed" to disk whenever an insert or update occurs. This to ensure data integrity.

I am interested in hearing some views about this subject, or has it been discussed to death already?

Anyway just some thoughts I'd like to share.

Marc Bellefeuille
SHL Systemhouse
Ottawa Ontario, Canada
e-mail: bellefm_at_shl.com
I Received on Mon Nov 14 1994 - 18:42:20 CET