Re: POC: converting Lists into arrays

David Rowley <david(dot)rowley(at)2ndquadrant(dot)com> writes:
> On Wed, 17 Jul 2019 at 11:06, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> (Actually, I doubt that any of these changes will really move the
>> performance needle in the real world. It's more a case of wanting
>> the code to present good examples not bad ones.)

> In spirit with the above, I'd quite like to fix a small bad example
> that I ended up with in nodeAppend.c and nodeMergeappend.c for
> run-time partition pruning.

I didn't test the patch, but just by eyeball it looks sane,
and I concur it should win if the bitmap is sparse.

One small question is whether it loses if most of the subplans
are present in the bitmap. I imagine that would be close enough
to break-even, but it might be worth trying to test to be sure.
(I'd think about breaking out just the loops in question and
testing them stand-alone, or else putting in an outer loop to
repeat them, since as you say the surrounding work probably
dominates.)

regards, tom lane