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

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