| From: | Peter Geoghegan <pg(at)heroku(dot)com> |
|---|---|
| To: | Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com> |
| Cc: | Pg Hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Using quicksort for every external sort run |
| Date: | 2016-03-24 02:36:10 |
| Message-ID: | CAM3SWZTbZ1At1wi_DMWwnVAGd7s8b9WpXv_7Bjn27APEamZTXQ@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Tue, Mar 22, 2016 at 2:27 PM, Tomas Vondra
<tomas(dot)vondra(at)2ndquadrant(dot)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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