On Thu, Jun 9, 2022 at 5:59 PM Thomas Munro <thomas.munro@gmail.com> wrote:
> That sounds nice, but introduces subtle problems for the planner. For
> example, pathkeys that look compatible might not be, when
> merge-joining an ICU 63 index scan against an ICU 67 index scan. You
> could teach it about that, whereas with my distinct OID concept they
> would already be considered non-matching automatically.
Right -- my proposal is likely to be more difficult to implement.
Seems like it might be worth going to the trouble of teaching the
planner about this difference, though.
That exact issue seems like the true underlying problem to me: we have
two sets of behaviors for a given collation, that are equivalent for
some purposes (the user thinks of them as totally interchangeable),
but not for other purposes (we can't expect old indexes to continue to
work with a new physical collation for their logical collation). So
directly tackling that seems natural to me.
--
Peter Geoghegan