unnesting of array of different size explodes memory - Mailing list pgsql-sql

<div class="WordSection1"><p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Times New
Roman","serif"">Hi,</span><pclass="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Times New
Roman","serif""> </span><pclass="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Times New
Roman","serif"">Ineed to sum up the elements of two arrays. Most arrays were of the same size, thus I just unnested the
arraysin one table and grouped the results in a loop for every row. When two arrays of different size (1200 and 1300)
wereprocessed, the memory usage exploded and the query was killed by the kernel.</span><p class="MsoNormal"><span
lang="EN-US"style="font-size:11.0pt;font-family:"Times New Roman","serif""> </span><p class="MsoNormal"><span
lang="EN-US"style="font-size:11.0pt;font-family:"Times New Roman","serif"">As I now understand, the following query
leadsto 12 results, not just 4 (or 3…):</span><p class="MsoNormal"><span lang="EN-US"
style="font-size:11.0pt;font-family:"TimesNew Roman","serif""> </span><p class="MsoNormal"><span lang="EN-US"
style="font-size:11.0pt;font-family:"TimesNew Roman","serif"">SELECT unnest(ARRAY[1,2,3]),
unnest(ARRAY[4,5,6,7]);</span><pclass="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Times New
Roman","serif""> </span><pclass="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Times New
Roman","serif"">Whycould postgres use as much memory till the kernel complained when unnesting 1200 and 1300 elements
resultingin 1.6e6 rows. Are there settings to prevent this such as “work_mem”?</span><p class="MsoNormal"><span
lang="EN-US"style="font-size:11.0pt;font-family:"Times New Roman","serif""> </span><p class="MsoNormal"><span
lang="EN-US"style="font-size:11.0pt;font-family:"Times New Roman","serif"">Regards,</span><p class="MsoNormal"><span
lang="EN-US"style="font-size:11.0pt;font-family:"Times New Roman","serif"">Andreas</span><p class="MsoNormal"><span
lang="EN-US"style="font-size:11.0pt;font-family:"Times New Roman","serif""> </span><p class="MsoNormal"><span
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