From: <ries@jongert.nl>
Cc: <pgsql-sql@postgresql.org>
Subject: Re: is this explain good or bad???
Date: Fri, 19 Sep 2003 10:02:32 +0200
Message-ID: <003101c37e84$61b54b80$fd01000a@IT001>
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Importance: Normal

Here are the explain analyze versions:


Best regards and thanx in advance
Ries


explain analyze select count(*) from sq_logfile;

NOTICE:  QUERY PLAN:
Aggregate  (cost=35988.07..35988.07 rows=1 width=0) (actual
time=71907.64..71907.64 rows=1 loops=1)
  ->  Seq Scan on sq_logfile  (cost=0.00..33493.86 rows=997686 width=0)
(actual time=12.90..46759.12 rows=997686 loops=1)
Total runtime: 71907.76 msec

explain analyze select count(*) from sq_flogile;
NOTICE:  QUERY PLAN:
Aggregate  (cost=128282.68..128282.68 rows=1 width=40) (actual
time=99338.92..99338.92 rows=1 loops=1)
  ->  Hash Join  (cost=8.65..125788.46 rows=997686 width=40) (actual
time=34.34..93123.02 rows=997686 loops=1)
        ->  Hash Join  (cost=6.49..105832.58 rows=997686 width=36) (actual
time=23.94..78411.62 rows=997686 loops=1)
              ->  Hash Join  (cost=4.75..88371.34 rows=997686 width=32)
(actual time=15.68..63115.86 rows=997686 loops=1)
                    ->  Hash Join  (cost=3.69..68416.56 rows=997686
width=28) (actual time=12.56..45110.94 rows=997686 loops=1)
                          ->  Hash Join  (cost=2.58..50955.94 rows=997686
width=24) (actual time=9.24..23160.42 rows=997686 loops=1)
                                ->  Seq Scan on sq_logfile sl
(cost=0.00..33493.86 rows=997686 width=20) (actual time=5.72..11518.14
rows=997686 loops=1)
                                ->  Hash  (cost=2.26..2.26 rows=126 width=4)
(actual time=3.46..3.46 rows=0 loops=1)
                                      ->  Seq Scan on sq_contenttypes ct
(cost=0.00..2.26 rows=126 width=4) (actual time=2.88..3.17 rows=126 loops=1)
                          ->  Hash  (cost=1.09..1.09 rows=9 width=4) (actual
time=3.21..3.21 rows=0 loops=1)
                                ->  Seq Scan on sq_requestmethods rm
(cost=0.00..1.09 rows=9 width=4) (actual time=3.16..3.19 rows=9 loops=1)
                    ->  Hash  (cost=1.05..1.05 rows=5 width=4) (actual
time=3.06..3.06 rows=0 loops=1)
                          ->  Seq Scan on sq_hierarchycodes hc
(cost=0.00..1.05 rows=5 width=4) (actual time=3.04..3.05 rows=5 loops=1)
              ->  Hash  (cost=1.59..1.59 rows=59 width=4) (actual
time=8.20..8.20 rows=0 loops=1)
                    ->  Seq Scan on sq_resultcodes rc  (cost=0.00..1.59
rows=59 width=4) (actual time=7.93..8.07 rows=59 loops=1)
        ->  Hash  (cost=1.93..1.93 rows=93 width=4) (actual
time=10.34..10.34 rows=0 loops=1)
              ->  Seq Scan on sq_clientaddrfqdn cafqdn  (cost=0.00..1.93
rows=93 width=4) (actual time=9.92..10.13 rows=93 loops=1)
Total runtime: 99339.49 msec


-----Oorspronkelijk bericht-----
Van: Tomasz Myrta [mailto:jasiek@klaster.net]
Verzonden: vrijdag 19 september 2003 8:52
Aan: ries@jongert.nl
CC: pgsql-sql@postgresql.org
Onderwerp: Re: [SQL] is this explain good or bad???


> explain select count(*) from sq_logfile;
Not too helpful.
Better choice is:
explain analyze select * from sq_logfile;

Your explains show that selecting from view is 4 times slower than
selecting from a table (35988:128282). It is possible.
Anyway counting 1 million rows usualy takes a long time...

Regards,
Tomasz Myrta