Re: Delete query takes exorbitant amount of time

From: Karim A Nassar <Karim(dot)Nassar(at)NAU(dot)EDU>
To: Stephan Szabo <sszabo(at)megazone(dot)bigpanda(dot)com>
Cc: Karim A Nassar <Karim(dot)Nassar(at)NAU(dot)EDU>, Simon Riggs <simon(at)2ndquadrant(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Christopher Kings-Lynne <chriskl(at)familyhealth(dot)com(dot)au>, pgsql-performance(at)postgresql(dot)org
Subject: Re: Delete query takes exorbitant amount of time
Date: 2005-03-28 16:37:01
Message-ID: Pine.SOL.4.21.0503280934160.831-100000@coruscant.cet.nau.edu
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On Mon, 28 Mar 2005, Stephan Szabo wrote:
> > On Mon, 28 Mar 2005, Simon Riggs wrote:
> > > run the EXPLAIN after doing
> > > SET enable_seqscan = off

...

> I think you have to prepare with enable_seqscan=off, because it
> effects how the query is planned and prepared.

orfs=# SET enable_seqscan = off;
SET
orfs=# PREPARE test2(int) AS SELECT 1 from measurement where
orfs-# id_int_sensor_meas_type = $1 FOR UPDATE;
PREPARE
orfs=# EXPLAIN ANALYZE EXECUTE TEST2(1); -- non-existent

QUERY PLAN
-------------------------------------------------------------------------
Index Scan using measurement__id_int_sensor_meas_type_idx on measurement
(cost=0.00..883881.49 rows=509478 width=6)
(actual time=29.207..29.207 rows=0 loops=1)
Index Cond: (id_int_sensor_meas_type = $1)
Total runtime: 29.277 ms
(3 rows)

orfs=# EXPLAIN ANALYZE EXECUTE TEST2(197); -- existing value

QUERY PLAN
-------------------------------------------------------------------------
Index Scan using measurement__id_int_sensor_meas_type_idx on measurement
(cost=0.00..883881.49 rows=509478 width=6)
(actual time=12.903..37478.167 rows=509478 loops=1)
Index Cond: (id_int_sensor_meas_type = $1)
Total runtime: 38113.338 ms
(3 rows)

--
Karim Nassar
Department of Computer Science
Box 15600, College of Engineering and Natural Sciences
Northern Arizona University, Flagstaff, Arizona 86011
Office: (928) 523-5868 -=- Mobile: (928) 699-9221

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