From: A. Kretschmer <andreas.kretschmer@schollglas.com>
To: pgsql-performance@postgresql.org
Subject: Re: Air-traffic benchmark
Date: Thu, 7 Jan 2010 14:32:25 +0100
Message-ID: <20100107133225.GB9884@a-kretschmer.de> (raw)
In-Reply-To: <852badbc1001070438j36eb10d3qa22398ffcbef405f@mail.gmail.com>
References: <852badbc1001070438j36eb10d3qa22398ffcbef405f@mail.gmail.com>
In response to Lefteris :
>
> airtraffic=# EXPLAIN ANALYZE SELECT "DayOfWeek", count(*) AS c FROM
> ontime WHERE "Year" BETWEEN 2000 AND 2008 GROUP BY "DayOfWeek" ORDER
> BY c DESC;
> QUERY
> PLAN
> ------------------------------------------------------------------------------------------------------------------------------------------
> Sort (cost=7407754.12..7407754.13 rows=4 width=2) (actual
> time=371188.821..371188.823 rows=7 loops=1)
> Sort Key: (count(*))
> Sort Method: quicksort Memory: 25kB
> -> HashAggregate (cost=7407754.04..7407754.08 rows=4 width=2)
> (actual time=371163.316..371163.320 rows=7 loops=1)
> -> Seq Scan on ontime (cost=0.00..7143875.40 rows=52775727
> width=2) (actual time=190938.959..346180.079 rows=52484047 loops=1)
> Filter: (("Year" >= 2000) AND ("Year" <= 2008))
> Total runtime: 371201.156 ms
> (7 rows)
>
>
> I understand that the problem here is the memory used by the sort
> method. *But*, I already changed the work_mem parameter to 6gigs:)
No.
The problem here is the Seq-Scan. It returns about 52.000.000 rows,
approximately roughly table, it needs 346 seconds.
The sort needs only 25 KByte and only 0.02ms.
Andreas
--
Andreas Kretschmer
Kontakt: Heynitz: 035242/47150, D1: 0160/7141639 (mehr: -> Header)
GnuPG: 0x31720C99, 1006 CCB4 A326 1D42 6431 2EB0 389D 1DC2 3172 0C99
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Reply to all the recipients using the --to and --cc options:
reply via email
To: pgsql-performance@postgresql.org
Cc: andreas.kretschmer@schollglas.com
Subject: Re: Air-traffic benchmark
In-Reply-To: <20100107133225.GB9884@a-kretschmer.de>
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
This inbox is served by DDX for PostgreSQL; see mirroring instructions
for how to clone and mirror all data and code used for this inbox