Re: Removing INNER JOINs

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Heikki Linnakangas <hlinnakangas(at)vmware(dot)com>
Cc: Robert Haas <robertmhaas(at)gmail(dot)com>, Stephen Frost <sfrost(at)snowman(dot)net>, 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 19:08:27
Message-ID: 22157.1417633707@sss.pgh.pa.us
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Heikki Linnakangas <hlinnakangas(at)vmware(dot)com> writes:
> Do you need to plan for every combination, where some joins are removed
> and some are not?

I would vote for just having two plans and one switch node. To exploit
any finer grain, we'd have to have infrastructure that would let us figure
out *which* constraints pending triggers might indicate transient
invalidity of, and that doesn't seem likely to be worth the trouble.

> I hope the same mechanism could be used to prepare a plan for a query
> with parameters, where the parameters might or might not allow a partial
> index to be used. We have some smarts nowadays to use custom plans, but
> this could be better.

Interesting thought, but that would be a totally different switch
condition ...

regards, tom lane

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