From: Kevin Kempter <kevin@kevinkempterllc.com>
To: pgsql-performance@postgresql.org
Subject: Re: Query only slow on first run
Date: Tue, 27 Nov 2007 09:57:07 -0700
Message-ID: <200711270957.07818.kevin@kevinkempterllc.com> (raw)
In-Reply-To: <fihgt1$1mmh$1@news.hub.org>
References: <fihgt1$1mmh$1@news.hub.org>
On Tuesday 27 November 2007 09:33:36 cluster wrote:
> I have a query that takes about 7000 ms in average to complete the first
> time it runs. Subsequent runs complete in only 50 ms. That is more than
> a factor 100 faster! How can I make the query perform good in the first
> run too?
>
> Query and output from both first and second run of Explain Analyze is
> pasted here:
>
> http://rafb.net/p/yrKyoA17.html
>
> ---------------------------(end of broadcast)---------------------------
> TIP 9: In versions below 8.0, the planner will ignore your desire to
> choose an index scan if your joining column's datatypes do not
> match
The query is faster the second run because the data pages were pulled into the
buffer pool during the first run. I would suggest using the explain plan from
the first run and test your changes on a recently started instance (or at
least on an instance where enough activity has transpired to effectively
rotate the buffer pages).
/Kevin
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To: pgsql-performance@postgresql.org
Cc: kevin@kevinkempterllc.com
Subject: Re: Query only slow on first run
In-Reply-To: <200711270957.07818.kevin@kevinkempterllc.com>
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