Peter Geoghegan <pg@bowt.ie> writes:
> I agree that "false positive" is not a valid way of describing a
> breaking change in a Postgres collation that happens to not affect one
> index in particular, due to the current phase of the moon. It's
> probably very likely that most individual indexes that we warn about
> will be so-called false positives.
This is not the concern that I have. I agree that if we tell a user
that collation X changed behavior and he'd better reindex his indexes
that use collation X, but none of them actually contain any cases that
changed behavior, that's not a "false positive" --- that's "it's cheaper
to reindex than to try to identify whether there's a problem". What
I mean by "false positive" is telling every macOS user that they'd better
reindex everything every year, when in point of fact Apple changes those
collations almost never. We will soon lose those users' attention ---
see fable about boy crying wolf --- and then when Apple actually does
change something, we've got a problem. So if we give collation-change
warnings, they'd better have some measurable connection to reality.
regards, tom lane