DROP SUBSCRIPTION, query cancellations and slot handling

Hi,

I have noticed the following behavior with DROP SUBSCRIPTION followed
by a cancel request. If the remote replication slot is dropped, the
subscription may still be present locally:
=# CREATE SUBSCRIPTION mysub CONNECTION 'port=5432 user=mpaquier
dbname=mpaquier' PUBLICATION mypub, insert_only;
NOTICE: 00000: created replication slot "mysub" on publisher
LOCATION: CreateSubscription, subscriptioncmds.c:408
NOTICE: 00000: synchronized table states
LOCATION: CreateSubscription, subscriptioncmds.c:434
CREATE SUBSCRIPTION
=# DROP SUBSCRIPTION mysub;
^CCancel request sent
NOTICE: 00000: dropped replication slot "mysub" on publisher
LOCATION: DropSubscription, subscriptioncmds.c:873
ERROR: 57014: canceling statement due to user request
LOCATION: ProcessInterrupts, postgres.c:2984

In this case the subscription is not dropped:
=# select subname from pg_subscription;
subname
---------
mysub
(1 row)
But trying to issue once again a drop results in an error:
=# DROP SUBSCRIPTION mysub;
ERROR: XX000: could not drop the replication slot "mysub" on publisher
DETAIL: The error was: ERROR: replication slot "mysub" does not exist
LOCATION: DropSubscription, subscriptioncmds.c:869

A subscription with the same name cannot be created either, so there
is nothing that the user can do except drop manually the slot on the
publisher. It seems to me that the moment where the slot is created
should be a point of no-return: the subcription has to be dropped on
the replication slot is dropped on the remote.

I am adding an open item.
Thanks,
--
Michael