out-of-order XID insertion in KnownAssignedXids (on 9.5.3)

Hi All,

we are running many postgresql master/slave setups. The slaves are
initialised from a pg_basebackup from the master and are sync streaming
from the master. When we determine the master has failed, the slave is
promoted. Some time after that, the old master is again initialised with a
pg_basebackup and starts streaming from the new master.

Our setup seems pretty "stock" and has been running for us for some years
(with different versions of postgresql but also different OSes).

Recently, we have gotten this error a fair amount of times: "out-of-order
XID insertion in KnownAssignedXids " when postgresql attempts to start
after being initialised with a pg_basebackup from the current master.

The only reference I can find on that particular error, is from 2012 and
the resulting issue is long fixed in our version of postgresql (9.5.3) ...
(
https://www.postgresql.org/message-id/201205230849.59825.andres@anarazel.de
)

Once the issue has occurred, a subsequent re-initialisation (with a
completely new pg_basebackup) does not resolve the issue.

I have a setup in the failing state, so I can produce any kind of log
mesages / details that would be helpful.

Thank you for your support,
Fredrik