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Re: Strangely Variable Query Performance

From: Steve <cheetah(at)tanabi(dot)org>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Scott Marlowe <smarlowe(at)g2switchworks(dot)com>, PostgreSQL Performance <pgsql-performance(at)postgresql(dot)org>
Subject: Re: Strangely Variable Query Performance
Date: 2007-04-12 23:40:15
Message-ID: Pine.GSO.4.64.0704121928440.17955@kittyhawk.tanabi.org (view raw or flat)
Thread:
Lists: pgsql-hackerspgsql-patchespgsql-performance
Table size: 16,037,728 rows

With enable_seqscan=off I get:

  Bitmap Heap Scan on detail_summary ds  (cost=4211395.20..4213045.32 
rows=1099 width=4)
    Recheck Cond: ((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[])))
    ->  Bitmap Index Scan on detail_summary_receipt_encounter_idx 
(cost=0.00..4211395.17 rows=1099 width=0)
          Index Cond: ((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[])))


The explain analyze is pending, running it now (however it doens't really 
appear to be any faster using this plan).


Steve

On Thu, 12 Apr 2007, Tom Lane wrote:

> Steve <cheetah(at)tanabi(dot)org> writes:
>> ... even if I force it to use the indexes
>> (enable_seqscan=off) it doesn't make it any faster really :/
>
> Does that change the plan, or do you still get a seqscan?
>
> BTW, how big is this table really (how many rows)?
>
> 			regards, tom lane
>
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