Re: proposal: Set effective_cache_size to greater of .conf value, shared_buffers - Mailing list pgsql-hackers

On 2014-05-07 11:45:04 -0700, Peter Geoghegan wrote:
> On Wed, May 7, 2014 at 11:38 AM, Andres Freund <andres@2ndquadrant.com> wrote:
> >> *) raising shared buffers does not 'give more memory to postgres for
> >> caching' -- it can only reduce it via double paging
> >
> > That's absolutely not a necessary consequence. If pages are in s_b for a
> > while the OS will be perfectly happy to throw them away.
> 
> The biggest problem with double buffering is not that it wastes
> memory. Rather, it's that it wastes memory bandwidth.

Doesn't match my experience. Even with the current buffer manager
there's usually enough locality to keep important pages in s_b for a
meaningful time. I *have* seen workloads that should have fit into
memory not fit because of double buffering.

Greetings,

Andres Freund

-- Andres Freund                       http://www.2ndQuadrant.com/PostgreSQL Development, 24x7 Support, Training &
Services