| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Andres Freund <andres(at)anarazel(dot)de> |
| Cc: | Adam Brusselback <adambrusselback(at)gmail(dot)com>, Petr Jelinek <petr(dot)jelinek(at)2ndquadrant(dot)com>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Discussion on missing optimizations |
| Date: | 2017-10-08 21:11:44 |
| Message-ID: | 15063.1507497104@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Andres Freund <andres(at)anarazel(dot)de> writes:
> On 2017-10-08 11:28:09 -0400, Tom Lane wrote:
>> https://commitfest.postgresql.org/15/1001/
>> The reason that's not in v10 is we haven't been able to convince
>> ourselves whether it's 100% correct.
> Unfortunately it won't help in this specific case (no support for UNION,
> just UNION ALL), but I thought it might be interesting to reference
> https://medium.com/@uwdb/introducing-cosette-527898504bd6
> here.
Huh, that is an interesting project indeed. Although I'm not sure that
it quite addresses the question of whether an optimization transform
is valid. IIUC, it could prove that a particular query having been fed
through the transform didn't change semantics, but that offers only
limited insight into whether some other query fed through the transform
might change.
regards, tom lane
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