On 2016-08-15 12:02:18 -0400, Robert Haas wrote:
> Thanks for taking a stab at this. I'd like to throw out a few concerns.
>
> One, I'm worried that adding an additional layer of pointer-jumping is
> going to slow things down and make Andres' work to speed up the
> executor more difficult. I don't know that there is a problem there,
> and if there is a problem I don't know what to do about it, but I
> think it's something we need to consider.
I'm quite concerned about that as well.
> I am somewhat inclined to
> believe that we need to restructure the executor in a bigger way so
> that it passes around datums instead of tuples; I'm inclined to
> believe that the current tuple-centric model is probably not optimal
> even for the existing storage format.
I actually prototyped that, and it's not an easy win so far. Column
extraction cost, even after significant optimization, is still often a
significant portion of the runtime. And e.g. projection only extracting
all columns, after evaluating a restrictive qual referring to an "early"
column, can be a significant win. We'd definitely have to give up on
extracting columns 0..n when accessing later columns... Hm.
Greetings,
Andres Freund
