Re: WIP: Upper planner pathification

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Robert Haas <robertmhaas(at)gmail(dot)com>
Cc: "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: WIP: Upper planner pathification
Date: 2016-03-08 17:18:40
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I wrote:
> There might be some other things we could do to provide a fast-path for
> particularly trivial cases.

I wanted to look into that before the code or tests had drifted far enough
to make comparisons dubious. Attached is a simple patch that lets
grouping_planner fall out with a minimum amount of work if the query is
just "SELECT expression(s)", and a couple of scatter plots of regression
test query timing. The first plot compares pre-pathification timing with
HEAD+this patch, and the second compares HEAD with HEAD+this patch.

I had hoped to see more of a benefit, actually, but it seems like this
might be enough of a win to be worth committing. Probably the main
argument against it is that we'd have to remember to maintain the list
of things-to-check-before-using-the-fast-path.


regards, tom lane

Attachment Content-Type Size
image/png 4.6 KB
image/png 4.5 KB
fast-path-for-select-expression.patch text/x-diff 1.8 KB

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