From: Andreas Gaab <A.Gaab@scanlab.de>
To: pgsql sql <pgsql-sql@postgresql.org>
Cc: Hans Joachim Münzer <H.Muenzer@scanlab.de>
Subject: unnesting of array of different size explodes memory
Date: Wed, 13 Apr 2011 11:15:38 +0200
Message-ID: <48DA836F3865C54B8FBF424A3B775AF667239FFDEF@Exchange-Server> (raw)
Hi,
I need to sum up the elements of two arrays. Most arrays were of the same size, thus I just unnested the arrays in one table and grouped the results in a loop for every row. When two arrays of different size (1200 and 1300) were processed, the memory usage exploded and the query was killed by the kernel.
As I now understand, the following query leads to 12 results, not just 4 (or 3...):
SELECT unnest(ARRAY[1,2,3]), unnest(ARRAY[4,5,6,7]);
Why could postgres use as much memory till the kernel complained when unnesting 1200 and 1300 elements resulting in 1.6e6 rows. Are there settings to prevent this such as "work_mem"?
Regards,
Andreas
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To: pgsql-sql@postgresql.org
Cc: A.Gaab@scanlab.de, H.Muenzer@scanlab.de
Subject: Re: unnesting of array of different size explodes memory
In-Reply-To: <48DA836F3865C54B8FBF424A3B775AF667239FFDEF@Exchange-Server>
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