| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Gregory Stark <stark(at)enterprisedb(dot)com> |
| Cc: | Simon Riggs <simon(at)2ndQuadrant(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, Kevin Grittner <Kevin(dot)Grittner(at)wicourts(dot)gov>, "jd\(at)commandprompt(dot)com" <jd(at)commandprompt(dot)com>, Josh Berkus <josh(at)agliodbs(dot)com>, Greg Smith <gsmith(at)gregsmith(dot)com>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: benchmarking the query planner |
| Date: | 2008-12-11 22:37:15 |
| Message-ID: | 12377.1229035035@sss.pgh.pa.us |
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Gregory Stark <stark(at)enterprisedb(dot)com> writes:
> Simon Riggs <simon(at)2ndQuadrant(dot)com> writes:
>> And I would like it even more if the sample size increased according to
>> table size, since that makes ndistinct values fairly random for large
>> tables.
> Unfortunately _any_ ndistinct estimate based on a sample of the table is going
> to be pretty random.
Yeah, it's a hard problem. It's worth noting though that increasing the
default stats target 10X is already going to result in a 10X increase in
the default sample size, so we should see at least some improvement in
the typical quality of ndistinct estimates.
regards, tom lane
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