Re: POC: converting Lists into arrays

David Rowley <david(dot)rowley(at)2ndquadrant(dot)com> writes:
> On Mon, 22 Jul 2019 at 02:45, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> 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.

> ...
> -- Test 2 (all matching subplans (8192 of them)) --

> Master version:

> Time: 14825.304 ms (00:14.825)
> Time: 14701.601 ms (00:14.702)
> Time: 14650.969 ms (00:14.651)

> Patched version:

> Time: 44551.811 ms (00:44.552)
> Time: 44357.915 ms (00:44.358)
> Time: 43454.958 ms (00:43.455)

> So the bms_next_member() loop is slower when the bitmapset is fully
> populated with all subplans, but way faster when there's just 1
> member.

Interesting. I wonder if bms_next_member() could be made any quicker?
Still, I agree that this is negligible compared to the actual work
needed per live subplan, and the fact that the cost scales per live
subplan is a good thing. So no objection to this patch, but a mental
note to take another look at bms_next_member() someday.

regards, tom lane