Re: Docs about buffers and sortmem setting

On Thu, Nov 14, 2002 at 12:20:49PM -0500, Neil Conway wrote:
> Well, part of the reason is that a lot of the data in shared_buffers
> has to be effectively duplicated in the kernel's I/O caches, because
> it's frequently accessed. So while I'd think the cost of fetching a
> page from the buffer pool is lower than from the OS' cache, increasing
> the size of the Postgres buffer pool effectively decreases the total
> amount of RAM available for caching.

Well, yes, but on a machine with 16 G and a data set < 16 G, that's
not the issue.  A 1G shared buffer is too big anyway, according to
our experience: it's fast at the beginning, but performance degrades.
I don't know why.

A

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