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Re: 2nd Level Buffer Cache

From: Robert Haas <robertmhaas(at)gmail(dot)com>
To: Kevin Grittner <Kevin(dot)Grittner(at)wicourts(dot)gov>
Cc: rsmogura <rsmogura(at)softperience(dot)eu>, PG Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: 2nd Level Buffer Cache
Date: 2011-03-18 16:19:47
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Lists: pgsql-hackers
On Fri, Mar 18, 2011 at 11:14 AM, Kevin Grittner
<Kevin(dot)Grittner(at)wicourts(dot)gov> wrote:
> Maybe the thing to focus on first is the oft-discussed "benchmark
> farm" (similar to the "build farm"), with a good mix of loads, so
> that the impact of changes can be better tracked for multiple
> workloads on a variety of platforms and configurations.  Without
> something like that it is very hard to justify the added complexity
> of an idea like this in terms of the performance benefit gained.

A related area that could use some looking at is why performance tops
out at shared_buffers ~8GB and starts to fall thereafter.  InnoDB can
apparently handle much larger buffer pools without a performance
drop-off.  There are some advantages to our reliance on the OS buffer
cache, to be sure, but as RAM continues to grow this might start to
get annoying.  On a 4GB system you might have shared_buffers set to
25% of memory, but on a 64GB system it'll be a smaller percentage, and
as memory capacities continue to clime it'll be smaller still.
Unfortunately I don't have the hardware to investigate this, but it's
worth thinking about, especially if we're thinking of doing things
that add more caching.

Robert Haas
The Enterprise PostgreSQL Company

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