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.
Thoughts?
regards, tom lane
