On 16/01/2020 17:12, Magnus Hagander wrote:
On Thu, Jan 16, 2020 at 6:08 PM Tom Lane <tgl@xxxxxxxxxxxxx> wrote:
Richard van der Hoff <richard@xxxxxxxxxx> 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.
Right, thanks to all who have suggested this.
It seems like a plausible explanation but it's worth noting that all the
indexed data here is (despite being in text columns), plain ascii. I'm
surprised that a change in collation rules would change the sorting of
such strings, and hence that it could lead to this problem. Am I naive?
To answer Adrian's question: the lengths of the values in the indexed
columns are identical between the duplicated rows.
