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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Robert Haas <robertmhaas@gmail.com>
Cc: David Rowley <david.rowley@2ndquadrant.com>
Cc: Amit Langote <Langote_Amit_f8@lab.ntt.co.jp>
Cc: Dmitry Dolgov <9erthalion6@gmail.com>
Cc: Jeff Janes <jeff.janes@gmail.com>
Cc: Ashutosh Bapat <ashutosh.bapat@enterprisedb.com>
Cc: Pavel Stehule <pavel.stehule@gmail.com>
Cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Subject: Re: why partition pruning doesn't work?
Date: Thu, 14 Jun 2018 10:40:11 -0400
Message-ID: <27099.1528987211@sss.pgh.pa.us> (raw)
In-Reply-To: <CA+TgmoajU5mPAvgGqST_iiW6P-Y2T3mAmSfCAw2GEtYi0KQCJg@mail.gmail.com>
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	<e6e751ea-0db4-0e7b-9513-97460edb60b3@lab.ntt.co.jp>
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	<CA+TgmoaQ+hxgDP4uxP_nRgC+JAn33_vona8P+GAnRDkceSZNSw@mail.gmail.com>
	<28597.1528900759@sss.pgh.pa.us>
	<ee1a67dc-69a1-b475-f812-3efe91509e32@lab.ntt.co.jp>
	<CAKJS1f-Dqc_J5=Ukkmr! kz_RoN_Lq+vzzppfDE51K7ACRo1rqqQ@mail.gmail.com>
	<CA+TgmoajU5mPAvgGqST_iiW6P-Y2T3mAmSfCAw2GEtYi0KQCJg@mail.gmail.com>

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




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