Strangely Variable Query Performance - Mailing list pgsql-performance
From | Steve |
---|---|
Subject | Strangely Variable Query Performance |
Date | |
Msg-id | Pine.GSO.4.64.0704121653030.17955@kittyhawk.tanabi.org Whole thread Raw |
In response to | Re: Slow Postgresql server (Jeff Frost <jeff@frostconsultingllc.com>) |
Responses |
Re: Strangely Variable Query Performance
Re: Strangely Variable Query Performance |
List | pgsql-performance |
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'. This query runs really slow [minutes] (query and explain below): select extract(epoch from ds.receipt) from detail_summary ds where ds.receipt >= '1998-12-30 0:0:0' and ds.encounter_id in (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) Results in the 'explain' : 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) Turning enable_seqscan to off results in a slightly more interesting explain, but an equally slow query. HOWEVER! The simple removal of the receipt date paramater results in a fast query, as such: select extract(epoch from ds.receipt) from detail_summary ds where ds.encounter_id in (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) This query returns instantly and explains as: Bitmap Heap Scan on detail_summary ds (cost=161.00..14819.81 rows=9963 width=4) Recheck Cond: (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_encounter_id_idx (cost=0.00..160.75 rows=9963 width=0) Index Cond: (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[])) Any thoughts? Both encounter_id and receipt date are indexed columns. I've vacuumed and analyzed the table. I tried making a combined index of encounter_id and receipt and it hasn't worked out any better. Thanks! Steve
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