[BUGS] Missing PRIMARY KEYs and duplicated rows

Hi all, we're encountering a very strange issue lately on a 9.4.5 server.

We recently performed a dump & restore of the entire cluster to
migrate to a new server.  All but one of the databases seem fine.
That one is encountering a very strange issue.

It seems that periodically, the primary keys (and underlying indexes)
of all tables in the database disappear, and every row in each table
gets duplicated.  This appears to occur at the storage level, as the
duplicated rows get their own ctids (so it's not just a query
artifact).  I've seen this happen twice in the past week.

I can delete the duplicate rows (by their ctid).  In the first
instance, I was unable to re-add the primary key, as it had reappeared
by the time I issued the statement.  In the most recent instance, I
did re-add the primary key to a table, and the other primary keys have
not yet re-appeared.

All indexes are b-tree indexes.  They were not created using
CONCURRENTLY.  They are in the default tablespace.  The installation
is on an Intel CentOS machine using the PGDG RPMs.  I've checked the
release notes for all 9.4 bugfixes and do not see anything which could
relate to this issue.

Any insight into this issue?  We will probably just drop and recreate
the database from the recent dump, as it is on a production server and
we'd rather not take chances tinkering around with it.  But it would
be nice to know why/how we've encountered this to ensure it won't
happen again, because frankly it's quite a scary issue.


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