| From: | David Rowley <dgrowleyml(at)gmail(dot)com> |
|---|---|
| To: | Dmitry Dolgov <9erthalion6(at)gmail(dot)com> |
| Cc: | Kyotaro Horiguchi <horikyota(dot)ntt(at)gmail(dot)com>, Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>, florisvannee(at)optiver(dot)com, pg(at)bowt(dot)ie, jesper(dot)pedersen(at)redhat(dot)com, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, Thomas Munro <thomas(dot)munro(at)gmail(dot)com>, jtc331(at)gmail(dot)com, rafia(dot)pghackers(at)gmail(dot)com, Jeff Janes <jeff(dot)janes(at)gmail(dot)com>, bhushan(dot)uparkar(at)gmail(dot)com, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>, Alexander Korotkov <a(dot)korotkov(at)postgrespro(dot)ru> |
| Subject: | Re: Index Skip Scan |
| Date: | 2020-03-10 22:17:51 |
| Message-ID: | CAApHDvo1NF0Qv9ZdnuDu03=1JwEq7GiVa-q3Qu=aMzmD9SV-vQ@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Wed, 11 Mar 2020 at 01:38, Dmitry Dolgov <9erthalion6(at)gmail(dot)com> wrote:
>
> > >On Tue, Mar 10, 2020 at 09:29:32AM +1300, David Rowley wrote:
> > There's also some weird looking assumptions that an EquivalenceMember
> > can only be a Var in create_distinct_paths(). I think you're only
> > saved from crashing there because a ProjectionPath will be created
> > atop of the IndexPath to evaluate expressions, in which case you're
> > not seeing the IndexPath. This results in the optimisation not
> > working in cases like:
>
> I've read it as "an assumption that an EquivalenceMember can only be a
> Var" results in "the optimisation not working in cases like this". But
> you've meant that ignoring a ProjectionPath with an IndexPath inside
> results in this optimisation not working, right? If so, then everything
> is clear, and my apologies, maybe I need to finally fix my sleep
> schedule :)
Yes, I was complaining that a ProjectionPath breaks the optimisation
and I don't believe there's any reason that it should.
I believe the way to make that work correctly requires paying
attention to the Path's uniquekeys rather than what type of path it
is.
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