Re: POC: converting Lists into arrays

Hi,

On 2019-03-04 16:28:40 -0500, Tom Lane wrote:
> Andres Freund <andres(at)anarazel(dot)de> writes:
> > I don't buy this. I think e.g. redisgning the way we represent
> > targetlists would be good (it's e.g. insane that we recompute
> > descriptors out of them all the time), and would reduce their allocator
> > costs.
>
> Maybe we're not on the same page here, but it seems to me that that'd be
> addressable with pretty localized changes (eg, adding more fields to
> TargetEntry, or keeping a pre-instantiated output tupdesc in each Plan
> node). But if the concern is about the amount of palloc bandwidth going
> into List cells, we're not going to be able to improve that with localized
> data structure changes; it'll take something like the patch I've proposed.

What I'm saying is that it'd be reasonable to replace the use of list
for targetlists with 'list2' without a wholesale replacement of all the
list code, and it'd give us benefits.

> I find it interesting that you get different results.

What I reported weren't vanilla pgbench -S results, so there's that
difference. If measure the DO loop based test I posted, do you see a
difference?

Greetings,

Andres Freund