Re: WIP: Faster Expression Processing v4

On 2017-03-15 15:41:22 -0400, Tom Lane wrote:
> Andres Freund <andres(at)anarazel(dot)de> writes:
> > On March 15, 2017 12:33:28 PM PDT, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> >> So for my money, you should drop 0002 altogether and just have 0004
> >> remove get_last_attnums() from execUtils.c and stick it into
> >> execExpr.c. I suppose you still need the LastAttnumInfo API change
> >> so as to decouple it from ProjectionInfo, but that's minor.
>
> > I think it's quite useful in other places too, we do repeated slot-getattrs in a bunch of places in the executor, and it's noticeable performance wise.
>
> Color me dubious. Which specific other places have you got in mind, and
> do they have expression trees at hand that would tell them which columns
> they really need to pull out?

I was thinking of execGrouping.c's execTuplesMatch(),
TupleHashTableHash() (and unequal, but doubt that matters
performancewise). There's also nodeHash.c's ExecHashGetValue(), but I
think that'd possibly better fixed differently.

Greetings,

Andres Freund