unnesting of array of different size explodes memory

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

___________________________________________________________________________

SCANLAB AG
Dr. Andreas Simon Gaab
Entwicklung * R & D

Siemensstr. 2a * 82178 Puchheim * Germany
Tel. +49 (89) 800 746-513 * Fax +49 (89) 800 746-199
mailto:a(dot)gaab(at)scanlab(dot)de * www.scanlab.de<http://www.scanlab.de>

Amtsgericht München: HRB 124707 * USt-IdNr.: DE 129 456 351
Vorstand: Georg Hofner (Sprecher), Christian Huttenloher, Norbert Petschik
Aufsichtsrat (Vorsitz): Dr. Hans J. Langer
___________________________________________________________________________

Besuchen Sie uns auf der / Meet us at
LASER World of PHOTONICS 2011
Munich, Germany
May 23 - 26, 2011
Hall C2, Booth 461