logical replication and PANIC during shutdown checkpoint in publisher

Hi,

When I shut down the publisher while I repeated creating and dropping
the subscription in the subscriber, the publisher emitted the following
PANIC error during shutdown checkpoint.

PANIC: concurrent transaction log activity while database system is
shutting down

The cause of this problem is that walsender for logical replication can
generate WAL records even during shutdown checkpoint.

Firstly walsender keeps running until shutdown checkpoint finishes
so that all the WAL including shutdown checkpoint record can be
replicated to the standby. This was safe because previously walsender
could not generate WAL records. However this assumption became
invalid because of logical replication. That is, currenty walsender for
logical replication can generate WAL records, for example, by executing
CREATE_REPLICATION_SLOT command. This is an oversight in
logical replication patch, I think.

To fix this issue, we should terminate walsender for logical replication
before shutdown checkpoint starts. Of course walsender for physical
replication still needs to keep running until shutdown checkpoint ends,
though.

Regards,

--
Fujii Masao