Jorel Casal <jcasal@ixl.com> writes:
> During a Patroni leader switchover, we had a situation where a unique index
> stopped "working", the index did not have records
> that were in fact in the table and the table had duplicate records which
> should have been prevented by said unique index.
If the index was on a string type (text/varchar), the most likely
explanation is a switch to a different OS version with inconsistent
collation rules. See
https://wiki.postgresql.org/wiki/Locale_data_changes
regards, tom lane