Re: Using quicksort for every external sort run - Mailing list pgsql-hackers

From Peter Geoghegan
Subject Re: Using quicksort for every external sort run
Date
Msg-id CAM3SWZTbZ1At1wi_DMWwnVAGd7s8b9WpXv_7Bjn27APEamZTXQ@mail.gmail.com
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In response to Re: Using quicksort for every external sort run  (Tomas Vondra <tomas.vondra@2ndquadrant.com>)
List pgsql-hackers
On Tue, Mar 22, 2016 at 2:27 PM, Tomas Vondra
<tomas.vondra@2ndquadrant.com> wrote:
> For example these two queries got almost 2x as slow for some data sets:
>
> SELECT a FROM numeric_test UNION SELECT a FROM numeric_test_padding
> SELECT a FROM text_test UNION SELECT a FROM text_test_padding
>
> I assume the slowdown is related to the batching (as it's only happening for
> low work_mem values), so perhaps there's an internal heuristics that we
> could tune?

Can you show trace_sort output for these cases? Both master, and patched?

Thanks
-- 
Peter Geoghegan



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