Re: fixing old_snapshot_threshold's time->xid mapping

On Tue, Apr 21, 2020 at 2:05 PM Thomas Munro <thomas.munro@gmail.com> wrote:
> As before, these two apply on top of Robert's patches (or at least his
> 0001 and 0002).

While trying to figure out if Robert's 0003 patch was correct, I added
yet another patch to this stack to test it.  0006 does basic xid map
maintenance that exercises the cases 0003 fixes, and I think it
demonstrates that they now work correctly.  Also some minor perl
improvements to 0005.  I'll attach 0001-0004 again but they are
unchanged.

Since confusion about head vs tail seems to have been at the root of
the bugs addressed by 0003, I wonder if we should also rename
head_{timestamp,offset} to oldest_{timestamp,offset}.