On Wed, May 7, 2014 at 2:49 PM, Andres Freund <andres@2ndquadrant.com> wrote:
> 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.
Same here.
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company