Re: Issue with logical replication slot during switchover

Hi Amit,

On Wed, 12 Nov 2025 at 05:22, Amit Kapila <amit.kapila16@gmail.com> wrote:

> It is difficult to tell when this can happen but you detailed there is
> a theoretical possibility of the same. If we had an in-core cluster
> tool that manages nodes on its own which doesn't allow such scenarios
> to happen then we could possibly say that using such a tool it is safe
> to overwrite old primary's slots.


That's a lot of ifs, and none of them could be fulfilled in the foreseeable
future.

Situation you describe is impossible.
When there is a split-brain and someone drops and re-creating logical slots
with the same names on the old primary - such node can't be joined as a
standby without pg_rewind.
In its current state pg_rewind wipes the pg_replslot directory, and
therefore there will be no replication slots.
That is, if there is a logical replication slot with failover=true and
synced=false on a healthy standby, it could have happened only because the
old primary was shut down gracefully.

Regards,
--
Alexander Kukushkin