| From: | Jeff Janes <jeff(dot)janes(at)gmail(dot)com> |
|---|---|
| To: | Josh Berkus <josh(at)agliodbs(dot)com> |
| Cc: | Peter Geoghegan <pg(at)heroku(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>, Robert Haas <robertmhaas(at)gmail(dot)com>, Claudio Freire <klaussfreire(at)gmail(dot)com>, Merlin Moncure <mmoncure(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 20:36:43 |
| Message-ID: | CAMkU=1wqP7h=Dp4tL5HSKAe9Jihn9RhgM6sVvevGekmGOgkqXQ@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Wed, May 7, 2014 at 11:04 AM, Josh Berkus <josh(at)agliodbs(dot)com> wrote:
> On 05/06/2014 10:35 PM, Peter Geoghegan wrote:
> > +1. In my view, we probably should have set it to a much higher
> > absolute default value. The main problem with setting it to any
> > multiple of shared_buffers that I can see is that shared_buffers is a
> > very poor proxy for what effective_cache_size is supposed to
> > represent. In general, the folk wisdom around sizing shared_buffers
> > has past its sell-by date.
>
> Unfortunately nobody has the time/resources to do the kind of testing
> required for a new recommendation for shared_buffers.
>
I think it is worse than that. I don't think we know what such testing
would even look like. SSD? BBU? max_connections=20000 with 256 cores?
pgbench -N? capture and replay of Amazon's workload?
If we could spell out/agree upon what kind of testing we would find
convincing, that would probably go a long way to getting some people to
work on carrying out the tests. Unless the conclusion was "please have 3TB
or RAM and a 50 disk RAID", then there might be few takers.
Cheers,
Jeff
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