From: Piotr Czekalski <pczekalski@techbaza.pl>
To: pgsql-sql@postgresql.org
Subject: Re: DELETE FROM takes forever
Date: Thu, 10 Feb 2011 19:36:51 +0100
Message-ID: <4D543043.70403@techbaza.pl> (raw)
In-Reply-To: <AANLkTim0z576Axfm4QWTTg_RXbdMgpppWC_rTF5ZzRoA@mail.gmail.com>
References: <AANLkTim0z576Axfm4QWTTg_RXbdMgpppWC_rTF5ZzRoA@mail.gmail.com>
Are your IDs (in both tables) a subject of index?
If so, analyze tables and indexes. If not, create an index for each ID -
that may help.
Post an explain plan of the query as well. I guess there is full scan
instead of index scan, thus running over and over 800 rows vs 110mln
rows may take a lot of time.
Hope that helps,
Piotr
W dniu 2011-02-10 18:57, Josh pisze:
> Hi
>
> I'm trying to do a DELETE FROM on my large table (about 800 million
> rows) based on the contents of another, moderately large table (about
> 110 million rows). The command I'm using is:
>
> DELETE FROM records WHERE id NOT IN (SELECT id FROM unique_records);
>
> This process ran for about two weeks before I decided to stop it -- it
> was dragging down the DB server. I can understand long-running
> processes, but two weeks seems a bit much even for a big table.
>
> Is this the best way to approach the problem? Is there a better way?
>
> Some background: The server is version 8.3, running nothing but Pg.
> The 'records' table has 'id' as its primary key, and one other index
> on another column. The table is referenced by just about every other
> table in my DB (about 15 other tables) via foreign key constraints,
> which I don't want to break (which is why I'm not just recreating the
> table rather than deleting rows). Most of the dependent tables have ON
> DELETE CASCADE. The 'unique_records' table is a temp table I got via
> something like: SELECT DISTINCT (other_column) id INTO unique_records
> FROM records
>
>
> Thanks very much!
>
> Josh Leder
>
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To: pgsql-sql@postgresql.org
Cc: pczekalski@techbaza.pl
Subject: Re: DELETE FROM takes forever
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