From: Tom Lane <tgl@sss.pgh.pa.us>
To: Robert Haas <robertmhaas@gmail.com>
cc: David Rowley <david.rowley@2ndquadrant.com>,
        Amit Langote <Langote_Amit_f8@lab.ntt.co.jp>,
        Dmitry Dolgov <9erthalion6@gmail.com>,
        Jeff Janes <jeff.janes@gmail.com>,
        Ashutosh Bapat <ashutosh.bapat@enterprisedb.com>,
        Pavel Stehule <pavel.stehule@gmail.com>,
        PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Subject: Re: why partition pruning doesn't work?
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Comments: In-reply-to Robert Haas <robertmhaas@gmail.com>
	message dated "Thu, 14 Jun 2018 08:40:13 -0400"
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Date: Thu, 14 Jun 2018 10:40:11 -0400
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Robert Haas <robertmhaas@gmail.com> writes:
> On Thu, Jun 14, 2018 at 7:23 AM, David Rowley
> <david.rowley@2ndquadrant.com> wrote:
>> However, I only spent about 10 mins looking into this, there may be
>> some giant holes in the idea.  It would need much more research.

> It kind of flies in the face of the idea that a RangeTblEntry is just
> a node that can be freely copied around, serialized and deserialized,
> etc.

And also the idea that the Plan tree is read-only to the executor,
which is not a good property to give up.

> I think it would be better to keep the pointer in the RelOptInfo in
> the planner and in the EState or PlanState in the executor.  Those are
> things we don't think can be copied, serialized, etc.

Yeah, RelOptInfo seems like the natural place in the planner; we might
need index relcache links in IndexOptInfo, too.

I'm less sure what to do in the executor.  We already do keep open
relation pointers in PlanStates; the problem is just that it's
node-type-specific (ss_currentRelation, iss_RelationDesc, etc).  Perhaps
that's unavoidable and we should just add more such fields as needed.

			regards, tom lane