Re: BUG #15285: Query used index over field with ICU collation in some cases wrongly return 0 rows

On Thu, 03 Sep 2020 13:49:24 -0400
Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

> =?UTF-8?Q?=D0=BE=D0=B2=D1=87=D0=B5=D0=BD=D0=BA=D0=BE" ?=
> <roman(dot)lytovchenko(at)gmail(dot)com>,
> "PostgreSQL mailing lists" <pgsql-bugs(at)lists(dot)postgresql(dot)org>
> Subject: Re: BUG #15285: Query used index over field with ICU collation in
> some cases wrongly return 0 rows In-reply-to:
> <c00a63d3-f9c3-4222-a659-637232523b30(at)manitou-mail(dot)org> References:
> <c00a63d3-f9c3-4222-a659-637232523b30(at)manitou-mail(dot)org> Comments: In-reply-to
> "Daniel Verite" <daniel(at)manitou-mail(dot)org> message dated "Thu, 03 Sep 2020
> 11:29:15 +0200" Fcc: inbox
> --------

Something broke in this answer, so I try to hook it back to the appropriate
thread.

> "Daniel Verite" <daniel(at)manitou-mail(dot)org> writes:
> > Now that we know that this collation is problematic, we could remove
> > this example, even if we don't want to go as far as documenting
> > ICU bugs. In fact bug reports used the same name "digitslast", so
> > I wonder if people tried this straight from our doc.
>
> If we aren't going to try to work around the bug, I agree that
> removing that example (or replacing it with a less buggy one?)
> is a good idea.

OK.
Please, find a patch in attachment. It removes the buggy collation from doc and
adapt existing ones to keep an example of combination of rules.

> I tend to agree with Peter that trying to work around a bug that
> isn't ours and that we don't fully understand is not going to
> be very productive. What is the argument, other than observation
> of a small number of test cases, that these other subroutines
> don't have bugs of their own?

What about adding it as a "known bug"/"will not fix" in
https://wiki.postgresql.org/wiki/Todo and link it from the doc in a note bloc? I
strongly feel most user do not know where to find such list of bugs in
PostgreSQL ecosystem.

Regards,