Horton

Re: Discussion on missing optimizations

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Adam Brusselback <adambrusselback@gmail.com>, Petr Jelinek <petr.jelinek@2ndquadrant.com>, Pg Hackers <pgsql-hackers@postgresql.org>
Date: 2017-10-08T16:18:04Z
Lists: pgsql-hackers 
On 2017-10-08 11:28:09 -0400, Tom Lane wrote:
> Adam Brusselback <adambrusselback@gmail.com> writes:
> > On another note:
> >> turning ORs into UNIONs
> 
> > This is another one which would be incredibly useful for me.  I've had
> > to do this manually for performance reasons far too often.
> 
> Well, maybe you could sign up to help review the open patch for that then:
> 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.

Greetings,

Andres Freund

Commits

  1. Reduce "X = X" to "X IS NOT NULL", if it's easy to do so.