| From: | Greg Stark <stark(at)mit(dot)edu> |
|---|---|
| To: | Gavin Flower <GavinFlower(at)archidevsys(dot)co(dot)nz> |
| Cc: | Peter Geoghegan <pg(at)heroku(dot)com>, Josh Berkus <josh(at)agliodbs(dot)com>, Simon Riggs <simon(at)2ndquadrant(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Kevin Grittner <kgrittn(at)ymail(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>, Jim Nasby <jim(at)nasby(dot)net> |
| Subject: | Re: ANALYZE sampling is too good |
| Date: | 2013-12-11 22:33:40 |
| Message-ID: | CAM-w4HN__RLfYhvtyBGDYFnmRZsyQXey4kZE-NUHggnC4NT0BA@mail.gmail.com |
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| Lists: | pgsql-hackers |
I think we're all wet here. I don't see any bias towards larger or smaller
rows. Larger tied will be on a larger number of pages but there will be
fewer of them on any one page. The average effect should be the same.
Smaller values might have a higher variance with block based sampling than
larger values. But that actually *is* the kind of thing that Simon's
approach of just compensating with later samples can deal with.
--
greg
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