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Re: proposal: Set effective_cache_size to greater of .conf value, shared_buffers

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Robert Haas <robertmhaas(at)gmail(dot)com>
Cc: 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: 2013-01-09 00:17:10
Message-ID: 5673.1357690630@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackers
Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> On Tue, Jan 8, 2013 at 9:53 AM, Claudio Freire <klaussfreire(at)gmail(dot)com> wrote:
>> Rather, I'd propose the default setting should be "-1" or something
>> "default" and "automagic" that works most of the time (but not all).

> A cruder heuristic that might be useful is 3 * shared_buffers.

Both parts of that work for me.  It's certainly silly that the default
value of effective_cache_size is now equivalent to the default value
of shared_buffers.  And I don't especially like the idea of trying to
make it depend directly on the box's physical RAM, for the same
practical reasons Robert mentioned.

It might be better to use 4 * shared_buffers, as that corresponds to the
multiple that's been the default since 8.2 or so (ie 128MB vs 32MB), and
3x just seems kinda oddball.

			regards, tom lane


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