Re: Update Unicode data to Unicode 16.0.0

On Mon, 2024-11-11 at 07:27 +0100, Peter Eisentraut wrote:
> Here is the patch to update the Unicode data to version 16.0.0.
> 
> Normally, this would have been routine, but a few months ago there
> was 
> some debate about how this should be handled. [0]  AFAICT, the
> consensus 
> was to go ahead with it, but I just wanted to notify it here to be
> clear.

We discussed $SUBJECT at the Developer Meeting before FOSDEM.

Those people who were most concerned about the Unicode updates on the
list were not present, so I don't consider the discussion to be
binding. But the attendees present agreed that:

  (a) we should not block the update to Unicode indefinitely; and
  (b) we should make reasonable attempts to mitigate potential
problems.

One idea for (b) resurfaced, which was to make a best-effort check at
pg_upgrade time for affected indexes. The check would not be
bulletproof, because we can't catch dependencies that are hidden inside
SPI (e.g. a plpgsql function that calls LOWER()), but it would catch
most potential problems.

Patch attached. A few notes:

  * The dependency entries don't exist because LOWER(), etc., are
system objects (pinned); so it queries the indexprs, indpreds,
partexprs, and conbin.
  * The query is large and perhaps too clever, but it seems to work. I
tried to add inline comments to the SQL, and pgindent had its own ideas
about how to format them -- suggestions welcome.
  * We haven't actually done the Unicode update yet, so it will notice
that the PG17 and PG18 Unicode versions are the same, and return early.
Either apply on top of the Unicode update patch, or comment out the
early return for testing.
  * It emits a warning rather than an error, so you need to specify
pg_upgrade with "-r" to see the output file.
  * I didn't adapt the query to run on pre-17 versions, even though it
could find some potential problem cases (like an index on NORMALIZE()).
I can add that if someone thinks it's worthwhile.

Regards,
	Jeff Davis