Re: [PERFORM] Working on huge RAM based datasets

[Jan Wieck]

On 7/9/2004 10:16 AM, Merlin Moncure wrote:
What is it about the buffer cache that makes it so unhappy being able
to
hold everything? I don't want to be seen as a cache hit fascist, but
isn't
it just better if the data is just *there*, available in the
postmaster's
address space ready for each backend process to access it, rather than
expecting the Linux cache mechanism, optimised as it may be, to have
to do
the caching?
The disk cache on most operating systems is optimized.  Plus, keeping
shared buffers low gives you more room to bump up the sort memory, which
will make your big queries run faster.
Plus, the situation will change dramatically with 7.5 where the disk 
cache will have less information than the PG shared buffers, which will 
become sequential scan resistant and will know that a block was pulled 
in on behalf of vacuum and not because the regular database access 
pattern required it.

Jan
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