From: Karim Nassar <karim.nassar@acm.org>
To: Stephan Szabo <sszabo@megazone.bigpanda.com>
Cc: Simon Riggs <simon@2ndquadrant.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Christopher Kings-Lynne <chriskl@familyhealth.com.au>
Cc: pgsql-performance@postgresql.org
Subject: Re: Delete query takes exorbitant amount of time
Date: Sat, 26 Mar 2005 17:44:47 -0700
Message-ID: <1111884288.27481.6.camel@k2.cet.nau.edu> (raw)
In-Reply-To: <20050326151658.D82144@megazone.bigpanda.com>
References: <1111709457.9085.127.camel@k2.cet.nau.edu>
<2630.1111711927@sss.pgh.pa.us>
<1111715131.9085.174.camel@k2.cet.nau.edu>
<3750.1111715318@sss.pgh.pa.us>
<4243879B.10200@familyhealth.com.au>
<20845.1111733900@sss.pgh.pa.us>
<1111763448.11750.730.camel@localhost.localdomain>
<1111787264.9168.7.camel@k2.cet.nau.edu>
<20050326075020.P63597@megazone.bigpanda.com>
<1111865788.9172.13.camel@k2.cet.nau.edu>
<20050326151658.D82144@megazone.bigpanda.com>
On Sat, 2005-03-26 at 15:18 -0800, Stephan Szabo wrote:
> On Sat, 26 Mar 2005, Karim Nassar wrote:
>
> > On Sat, 2005-03-26 at 07:55 -0800, Stephan Szabo wrote:
> > > That seems like it should be okay, hmm, what does something like:
> > >
> > > PREPARE test(int) AS SELECT 1 from measurement where
> > > id_int_sensor_meas_type = $1 FOR UPDATE;
> > > EXPLAIN ANALYZE EXECUTE TEST(1);
> > >
> > > give you as the plan?
> >
> > QUERY PLAN
> > -----------------------------------------------------------------------------------------------------------------------
> > Seq Scan on measurement (cost=0.00..164559.16 rows=509478 width=6)
> > (actual time=11608.402..11608.402 rows=0 loops=1)
> > Filter: (id_int_sensor_meas_type = $1)
> > Total runtime: 11608.441 ms
> > (3 rows)
>
> Hmm, has measurement been analyzed recently? You might want to see if
> raising the statistics target on measurement.id_int_sensor_meas_type and
> reanalyzing changes the estimated rows down from 500k.
orfs=# ALTER TABLE measurement ALTER COLUMN id_int_sensor_meas_type SET STATISTICS 1000;
ALTER TABLE
orfs=# VACUUM FULL ANALYZE VERBOSE;
<snip>
INFO: free space map: 52 relations, 13501 pages stored; 9760 total pages needed
DETAIL: Allocated FSM size: 1000 relations + 300000 pages = 1864 kB shared memory.
VACUUM
orfs=# PREPARE test(int) AS SELECT 1 from measurement where
orfs-# id_int_sensor_meas_type = $1 FOR UPDATE;
PREPARE
orfs=# EXPLAIN ANALYZE EXECUTE TEST(1);
QUERY PLAN
---------------------------------------------------------------------------------------------------------------------
Seq Scan on measurement (cost=0.00..164559.16 rows=509478 width=6) (actual time=8948.452..8948.452 rows=0 loops=1)
Filter: (id_int_sensor_meas_type = $1)
Total runtime: 8948.494 ms
(3 rows)
orfs=# EXPLAIN ANALYZE EXECUTE TEST(1);
QUERY PLAN
---------------------------------------------------------------------------------------------------------------------
Seq Scan on measurement (cost=0.00..164559.16 rows=509478 width=6) (actual time=3956.616..3956.616 rows=0 loops=1)
Filter: (id_int_sensor_meas_type = $1)
Total runtime: 3956.662 ms
(3 rows)
Some improvement. Even better once it's cached. Row estimate didn't
change. Is this the best I can expect? Is there any other optimizations
I am missing?
TIA,
--
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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To: pgsql-performance@postgresql.org
Cc: karim.nassar@acm.org, sszabo@megazone.bigpanda.com, simon@2ndquadrant.com, tgl@sss.pgh.pa.us, chriskl@familyhealth.com.au
Subject: Re: Delete query takes exorbitant amount of time
In-Reply-To: <1111884288.27481.6.camel@k2.cet.nau.edu>
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