| From: | Peter Geoghegan <pg(at)heroku(dot)com> |
|---|---|
| To: | Greg Stark <stark(at)mit(dot)edu> |
| Cc: | Simon Riggs <simon(at)2ndquadrant(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, Jeff Janes <jeff(dot)janes(at)gmail(dot)com>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org>, Heikki Linnakangas <hlinnaka(at)iki(dot)fi>, David Rowley <david(dot)rowley(at)2ndquadrant(dot)com> |
| Subject: | Re: Using quicksort for every external sort run |
| Date: | 2015-12-15 03:33:05 |
| Message-ID: | CAM3SWZTDWJYyqFvVCd3fVdtgUb1tg7COkS6F=LxOGPefH4s1mw@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Mon, Dec 14, 2015 at 7:22 PM, Peter Geoghegan <pg(at)heroku(dot)com> wrote:
> Thanks for taking the time to benchmark the patch!
Also, I should point out that you didn't add work_mem past the point
where the master branch will get slower, while the patch continues to
get faster. This seems to happen fairly reliably, certainly if
work_mem is sized at about 1GB, and often at lower settings. With the
POWER7 "Hydra" server, external sorting for a CREATE INDEX operation
could put any possible maintenance_work_mem setting to good use -- my
test case got faster with a 15GB maintenance_work_mem setting (the
server has 64GB of ram). I think I tried 25GB as a
maintenance_work_mem setting next, but started to get OOM errors at
that point.
Again, I point this out because I want to account for why my numbers
were better (for the benefit of other people -- I think you get this,
and are being fair).
--
Peter Geoghegan
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