Re: enable_joinremoval

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Robert Haas <robertmhaas(at)gmail(dot)com>
Cc: Greg Smith <greg(at)2ndquadrant(dot)com>, Simon Riggs <simon(at)2ndquadrant(dot)com>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: enable_joinremoval
Date: 2010-03-29 16:17:54
Message-ID: 14825.1269879474@sss.pgh.pa.us
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Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> On Mon, Mar 29, 2010 at 12:03 PM, Greg Smith <greg(at)2ndquadrant(dot)com> wrote:
>> at the top of my list in this area for 9.1 is to track down the rumored
>> patch that exports information about the rejected plans considered and get
>> that comitted. That always seems what I want to look at for answering the
>> question "why this plan instead of what I was expecting?"

> Having looked at that patch, I am skeptical of it, but we can
> certainly take a fresh look.

The problem with this line of thought is that it imagines you can look
at worked-out alternative plans. You can't, because the planner doesn't
pursue rejected alternatives that far (and you'd not want to wait long
enough for it to do so...)

regards, tom lane

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