Re: Collation versioning

On Tue, Sep 15, 2020 at 2:26 PM Peter Eisentraut
<peter(dot)eisentraut(at)2ndquadrant(dot)com> wrote:
>
> On 2020-09-08 16:45, Julien Rouhaud wrote:
> > I usually agree with that approach, I'm just afraid that getting a consensus on
> > the best way to do that will induce a lot of discussions, while this is
> > probably a corner case due to general usage of hash and bloom indexes.
> >
> > Anyway, in order to make progress on that topic I attach an additional POC
> > commit to add the required infrastructure to handle this case in
> > v29-0001-Add-a-new-amnostablecollorder-flag-in-IndexAmRou.patch.
>
> I'm confused now. I think we had mostly agreed on the v28 patch set,
> without this additional AM flag. There was still some discussion on
> what the AM flag's precise semantics should be. Do we want to work that
> out first?

That was my understanding too, but since Michael raised a concern I
wrote some initial implementation for that part. I'm assuming that
this new flag will raise some new discussion, and I hope this can be
discussed later, or at least in parallel, without interfering with the
rest of the patchset.

> Btw., I'm uneasy about the term "stable collation order". "Stable" has
> an established meaning for sorting. It's really about whether the AM
> uses collations at all, right?

Well, at the AM level I guess it's only about whether it's using some
kind of sorting or not, as the collation information is really at the
opclass level. It makes me realize that this approach won't be able
to cope with an index built using (varchar|text)_pattern_ops, and
that's probably something we should handle correctly.