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Re: effective_cache_size less than shared_buffers

From: Harald Armin Massa <chef(at)ghum(dot)de>
To: Greg Stark <stark(at)enterprisedb(dot)com>
Cc: jd(at)commandprompt(dot)com, Josh Berkus <josh(at)agliodbs(dot)com>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: effective_cache_size less than shared_buffers
Date: 2009-02-26 09:14:55
Message-ID: e3e180dc0902260114q2a350dbax5aa65fd3345e694b@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-hackers
Greg,

>
> Well we won't eliminate any problems unless we actually override the
> effective_cache_size setting by clipping it to shared_buffers. I don't
> really see much of a problem doing that. The only case where that
> would annoy someone was if they're intentionally understating
> effective_cache_size to push the planner into avoiding nested loops
> and I doin't think it's a powerful enough knob to be very likely used
> that way.
>

My experience from PostgreSQL on Windows: effective_cache_size should
reflect the value of "system cache" from task manager. shared_buffers (on
windows) should be rather small.

My real-workload-tests (no benchmarks, real usage of DB-Server) showed that
big shared buffers on Windows have a negative effect on PostgreSQL
performance. I have found no explanation WHY it is this way.

Harald


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