Robert Haas <robertmhaas@gmail.com> writes:
> Well, part of the problem is that I've not had a lot of luck trying to
> understand how the executor really works (what's a tuple table slot
> and why do we need to know in advance how many of them there are?).
You know, that's actually a really good question. There is not, as far
as I can see, much advantage to keeping the Slots in an array. We could
perfectly well keep them in a List and eliminate the notational overhead
of having to count them in advance. There'd be a bit more palloc
overhead (for the list cells) but avoiding the counting work would more
or less make up for that.
regards, tom lane