From: Tom Lane <tgl@sss.pgh.pa.us>
To: Kurt Overberg <kurt@hotdogrecords.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: Weird 8.2.4 performance
Date: Thu, 07 Jun 2007 09:32:31 -0400
Message-ID: <29877.1181223151@sss.pgh.pa.us> (raw)
In-Reply-To: <C040B179-DBCF-441F-9677-E03AE663CEF9@hotdogrecords.com>
References: <371D1936-E96B-4865-AEEF-C82AC41C2982@hotdogrecords.com>
<46674AEF.6040803@paradise.net.nz>
<4667CE87.30101@archonet.com>
<C040B179-DBCF-441F-9677-E03AE663CEF9@hotdogrecords.com>
Kurt Overberg <kurt@hotdogrecords.com> writes:
> ... Turning off bitmap scans definitely seems
> to help things,
I really seriously doubt that. On queries like this, where each inner
scan is fetching a couple hundred rows, the small extra overhead of a
bitmap scan should easily pay for itself. I think you're looking
entirely at caching effects that allow a re-read of the same data to
go faster.
You might try running the same query plan several times in a row and
noting the lowest time, then repeat for the other query plan. This will
get you comparable fully-cached times, which I bet will be very close
to the same.
regards, tom lane
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To: pgsql-performance@postgresql.org
Cc: tgl@sss.pgh.pa.us, kurt@hotdogrecords.com
Subject: Re: Weird 8.2.4 performance
In-Reply-To: <29877.1181223151@sss.pgh.pa.us>
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