Re: Inexplicable duplicate rows with unique constraint

On Thu, Jan 16, 2020 at 6:08 PM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>
> Richard van der Hoff <richard(at)matrix(dot)org> writes:
> > I'm trying to track down the cause of some duplicate rows in a table
> > which I would expect to be impossible due to a unique constraint. I'm
> > hoping that somebody here will be able to suggest something I might have
> > missed.
>
> Since these are text columns, one possibility you should be looking into
> is that the indexes have become corrupt due to a change in the operating
> system's sorting rules for the underlying locale. I don't recall details
> at the moment, but I do remember that a recent glibc update changed the
> sorting rules for some popular locale settings. If an installation had
> applied such an update underneath an existing database, you'd have a
> situation where existing entries in an index are not in-order according
> to the new behavior of the text comparison operators, leading to havoc
> because btree searching relies on the entries being correctly sorted.

See https://wiki.postgresql.org/wiki/Locale_data_changes for hints on
which linux distros updated when.

--
Magnus Hagander
Me: https://www.hagander.net/
Work: https://www.redpill-linpro.com/