| From: | Teodor Sigaev <teodor(at)sigaev(dot)ru> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, David Rowley <david(dot)rowley(at)2ndquadrant(dot)com> |
| Cc: | Alexander Korotkov <a(dot)korotkov(at)postgrespro(dot)ru>, Pgsql Hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: convert EXSITS to inner join gotcha and bug |
| Date: | 2017-04-29 17:35:05 |
| Message-ID: | ead7502c-a0bf-641e-6ebd-69dddb9165a5@sigaev.ru |
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| Thread: | |
| Lists: | pgsql-hackers |
> Really, the way to fix Teodor's complaint is to recognize that the
> semijoin inner rel is effectively unique against the whole outer rel,
> and then strength-reduce the semijoin to a plain join. The infrastructure
> we built for unique joins is capable of proving that, we just weren't
> applying it in the right way.
Perfect, it works. Thank you! Second patch reduces time of full query (my
example was just a small part) from 20 minutes to 20 seconds.
> I'm kind of strongly tempted to apply the second patch; but it would
> be fair to complain that reduce_unique_semijoins() is new development
> and should wait for v11. Opinions?
Obviously, I'm voting for second patch applied to version 10.
--
Teodor Sigaev E-mail: teodor(at)sigaev(dot)ru
WWW: http://www.sigaev.ru/
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