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Re: Strangely Variable Query Performance

From: Scott Marlowe <smarlowe(at)g2switchworks(dot)com>
To: Steve <cheetah(at)tanabi(dot)org>
Cc: PostgreSQL Performance <pgsql-performance(at)postgresql(dot)org>
Subject: Re: Strangely Variable Query Performance
Date: 2007-04-12 21:52:04
Message-ID: 1176414724.13754.23.camel@state.g2switchworks.com (view raw or flat)
Thread:
Lists: pgsql-hackerspgsql-patchespgsql-performance
On Thu, 2007-04-12 at 16:03, Steve wrote:
> Hey there;
> 
> On a Postgres 8.2.3 server, I've got a query that is running very slow in 
> some cases.  With some work, I've determined the 'slow part' of the query. 
> :)  This is a query on a table with like 10 million rows or something like 
> that.  encounter_id is an integer and receipt is of type 'date'.

SNIP

>   Seq Scan on detail_summary ds  (cost=0.00..1902749.83 rows=9962 width=4)
>     Filter: ((receipt >= '1998-12-30'::date) AND (encounter_id = ANY 
> ('{8813186,8813187,8813188,8813189,8813190,8813191,8813192,8813193,8813194,8813195,8813196,8813197,8813198,8813199,8813200,8813201,8813202,8813203,8813204,8813205,8813206,8813207,8813208,8813209,8813210,8813211,8813212,8813213,8813214,8813215,8813216,8813217,8813218,8813219,8813220,8813221,8813222,8813223,8813224,8813225,8813226,8813227,8813228,8813229,8813230,8813231,8813232,8813233,8813234,8813235,8813236,8813237,8813238,8813239,8813240,8813241,8813242,8813243,8813244,8813245,8813246,8813247,8813248,8813249,8813250,8813251,8813252,8813253,8813254,8813255,8813256,8813257,8813258,8813259,8813260,8813261,8813262,8813263,8813264,8813265,8813266,8813267,8813268,8813269,8813270,8813271,8813272,8813273,8813274,8813275,8813276,8813277,8813278,8813279,8813280,8813281,8813282,8813283,8813284,8815534}'::integer[])))
> (2 rows)

How accurate is the row estimate made by the planner?  (explain analyze
to be sure)

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