From: | Andres Freund <andres(at)2ndquadrant(dot)com> |
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To: | Noah Misch <noah(at)leadboat(dot)com> |
Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, David Rowley <dgrowleyml(at)gmail(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>, Dilip kumar <dilip(dot)kumar(at)huawei(dot)com> |
Subject: | Re: Allowing join removals for more join types |
Date: | 2014-06-05 00:12:33 |
Message-ID: | 20140605001233.GB2789@awork2.anarazel.de |
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Lists: | pgsql-hackers |
On 2014-06-04 20:04:07 -0400, Noah Misch wrote:
> On Wed, Jun 04, 2014 at 10:14:42AM -0400, Tom Lane wrote:
> > It's possible that we could apply the optimization only to queries that
> > have been issued directly by a client, but that seems rather ugly and
> > surprise-filled.
>
> ... such as this idea. It's a good start to a fairly-hard problem. FKs are
> also always valid when afterTriggers->query_depth == -1, such as when all
> ongoing queries qualified for EXEC_FLAG_SKIP_TRIGGERS. What else? We could
> teach trigger.c to efficiently report whether a given table has a queued RI
> trigger. Having done that, when plancache.c is building a custom plan, the
> planner could ignore FKs with pending RI checks and use the rest. At that
> point, the surprises will be reasonably-isolated.
A bit more crazy, but how about trying trying to plan joins with a added
one-time qual that checks the size of the deferred trigger queue? Then
we wouldn't even need special case plans.
Greetings,
Andres Freund
--
Andres Freund http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
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