Re: POC: converting Lists into arrays

On Mon, 22 Jul 2019 at 16:37, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>
> David Rowley <david(dot)rowley(at)2ndquadrant(dot)com> writes:
> > 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?

I had a quick look earlier and the only thing I saw was maybe to do
the first loop differently from subsequent ones. The "w &= mask;"
does nothing useful once we're past the first bitmapword that the loop
touches. Not sure what the could would look like exactly yet, or how
much it would help. I'll maybe experiment a bit later, but as separate
work from the other patch.

> 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.

Thanks for having a look. I'll have another look and will likely push
this a bit later on today if all is well.

--
David Rowley http://www.2ndQuadrant.com/
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