From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | Stephen Frost <sfrost(at)snowman(dot)net> |
Cc: | Atri Sharma <atri(dot)jiit(at)gmail(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, Andres Freund <andres(at)2ndquadrant(dot)com>, David Rowley <dgrowleyml(at)gmail(dot)com>, Mart Kelder <mart(at)kelder31(dot)nl>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>, Simon Riggs <simon(at)2ndquadrant(dot)com> |
Subject: | Re: Removing INNER JOINs |
Date: | 2014-12-03 18:08:08 |
Message-ID: | 20454.1417630088@sss.pgh.pa.us |
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Stephen Frost <sfrost(at)snowman(dot)net> writes:
> * Atri Sharma (atri(dot)jiit(at)gmail(dot)com) wrote:
>> Agreed, but in some cases, we could possibly make some assumptions (if
>> there is no index, if a large fraction of table will be returned in scan,
>> FunctionScan).
> All neat ideas but how about we get something which works in the way
> being asked for before we start trying to optimize it..? Maybe I'm
> missing something, but getting all of this infrastructure into place and
> making sure things aren't done to the plan tree which shouldn't be (or
> done to all of them if necessary..) is enough that we should get that
> bit done first and then worry if there are ways we can further improve
> things..
Yeah; moreover, there's no evidence that hard-wiring such assumptions
would save anything. In the example of a FunctionScan, guess what:
there's only one Path for that relation anyway.
I think the right approach for now is to emulate the GEQO precedent as
closely as possible. Build all the single-relation Paths the same as
now, then do a join search over all the relations, then (if we've noticed
that some joins are potentially removable) do another join search over
just the nonremovable relations.
regards, tom lane
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