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Re: Shared buffers, db transactions commited, and write IO on Solaris

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Erik Jones <erik(at)myemma(dot)com>
Cc: PostgreSQL Performance <pgsql-performance(at)postgresql(dot)org>
Subject: Re: Shared buffers, db transactions commited, and write IO on Solaris
Date: 2007-03-29 16:16:36
Message-ID: 23286.1175184996@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-performance
Erik Jones <erik(at)myemma(dot)com> writes:
> We've recently made a couple changes to our system that have resulted  
> in a drastic increase in performance as well as some very confusing  
> changes to the database statistics, specifically  
> pg_stat_database.xact_commit.  Here's the details:

I'm kinda boggled too.  I can see how increasing shared buffers could
result in a drastic reduction in write rate, if the working set of your
queries fits in the new space but didn't fit in the old.  I have no idea
how that leads to a drop in number of transactions committed though.
It doesn't make sense that autovac would run less frequently, because
it's driven by number of tuples changed not number of disk writes; and
that could hardly account for a 10x drop anyway.

Did you by any chance take note of exactly which processes were
generating all the I/O or the CPU load?

			regards, tom lane

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Subject: Re: Shared buffers, db transactions commited, and write IO on Solaris
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Subject: Re: Sunfire X4500 recommendations

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