| From: | Greg Stark <stark(at)mit(dot)edu> |
|---|---|
| To: | Peter Geoghegan <pg(at)heroku(dot)com> |
| Cc: | Jeff Janes <jeff(dot)janes(at)gmail(dot)com>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org>, Heikki Linnakangas <hlinnaka(at)iki(dot)fi>, Robert Haas <robertmhaas(at)gmail(dot)com>, Simon Riggs <simon(at)2ndquadrant(dot)com> |
| Subject: | Re: Using quicksort for every external sort run |
| Date: | 2015-12-01 01:12:13 |
| Message-ID: | CAM-w4HMBpLLs1HiuiSz3MnGB9B9XVcJxpNGAeJeawOLpB-zEqw@mail.gmail.com |
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| Lists: | pgsql-hackers |
Hm. Here is a log-log chart of those results (sorry for html mail). I'm not
really sure if log-log is the right tool to use for a O(nlog(n)) curve
though.
I think the take-away is that this is outside the domain where any
interesting break points occur. Maybe run more tests on the low end to find
where the tapesort can generate a single tape and avoid the merge and see
where the discontinuity is with quicksort for the various work_mem sizes.
And can you calculate an estimate where the domain would be where multiple
passes would be needed for this table at these work_mem sizes? Is it
feasible to test around there?
[image: Inline image 1]
--
greg
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