| From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
|---|---|
| To: | Andres Freund <andres(at)2ndquadrant(dot)com> |
| Cc: | Peter Geoghegan <pg(at)heroku(dot)com>, Merlin Moncure <mmoncure(at)gmail(dot)com>, Josh Berkus <josh(at)agliodbs(dot)com>, Simon Riggs <simon(at)2ndquadrant(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Bruce Momjian <bruce(at)momjian(dot)us>, Magnus Hagander <magnus(at)hagander(dot)net>, Andrew Dunstan <andrew(at)dunslane(dot)net>, Claudio Freire <klaussfreire(at)gmail(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: proposal: Set effective_cache_size to greater of .conf value, shared_buffers |
| Date: | 2014-05-07 18:50:53 |
| Message-ID: | CA+Tgmoa+jd=XmoB1=x_a9O98ARuAuESTn0hKnet69DPft7JAxA@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Wed, May 7, 2014 at 2:49 PM, Andres Freund <andres(at)2ndquadrant(dot)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(at)2ndquadrant(dot)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
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