Re: upper planner path-ification

On Sun, May 17, 2015 at 12:11 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Rather than adding tlists per se to Paths, I've been vaguely toying with
> a notion of identifying all the "interesting" subexpressions in a query
> (expensive functions, aggregates, etc), giving them indexes 1..n, and then
> marking Paths with bitmapsets showing which interesting subexpressions
> they can produce values for. This would make things like "does this Path
> compute all the needed aggregates" much cheaper to deal with than a raw
> tlist representation would do. But maybe that's still not the best way.

I don't know, but it seems like this might be pulling in the opposite
direction from your previously-stated desire to get subquery_planner
to output Paths rather than Plans as soon as possible. I'm inclined
to think that we need to make a start on this in whatever way is
simplest, and then refine it later. Adding tlists to (some?) paths
might not be the most beautiful way to get there, but there's a lot of
important stuff piling up behind making some kind of a start on this
refactoring, and we can't just keep postponing all of that stuff
indefinitely. Or if we do, the project as a whole will be worse off
for it, I think.

--
Robert Haas
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