Re: POC: converting Lists into arrays

Here's a rebased version of the main patch.

David Rowley <david(dot)rowley(at)2ndquadrant(dot)com> writes:
> The only thing that I did to manage to speed the patch up was to ditch
> the additional NULL test in lnext(). I don't see why that's required
> since lnext(NULL) would have crashed with the old implementation.

I adopted this idea. I think at one point where I was fooling with
different implementations for foreach(), it was necessary that lnext()
be cool with a NULL input; but as things stand now, it's not.

I haven't done anything else in the performance direction, but am
planning to play with that next.

I did run through all the list_delete_foo callers and fix the ones
that were still busted. I also changed things so that with
DEBUG_LIST_MEMORY_USAGE enabled, list deletions would move the data
arrays around, in hopes of catching more stale-pointer problems.
Depressingly, check-world still passed with that added, even before
I'd fixed the bugs I found by inspection. This does not speak well
for the coverage of our regression tests.

regards, tom lane