Re: Minimal logical decoding on standbys

Also, in the updated patch (v11), I have added some scenarios that
verify that slot is dropped when either master wal_level is
insufficient, or when slot is conflicting. Also organized the test
file a bit.

One scenario where replication slot removed even after fixing the problem (which Error message suggested to do)

Please refer this below scenario
Master cluster-
postgresql,conf file
wal_level=logical
hot_standby_feedback = on
port=5432

Standby cluster-
postgresql,conf file
wal_level=logical
hot_standby_feedback = on
port=5433

both Master/Slave cluster are up and running and are in SYNC with each other
Create a logical replication slot on SLAVE ( SELECT * from   pg_create_logical_replication_slot('m', 'test_decoding'); )

change wal_level='hot_standby' on Master postgresql.conf file / restart the server
Run get_changes function on Standby -
postgres=# select * from pg_logical_slot_get_changes('m',null,null);
ERROR:  logical decoding on standby requires wal_level >= logical on master

Correct it on Master postgresql.conf file ,i.e set  wal_level='logical'  again / restart the server
and again fire  get_changes function on Standby -
postgres=# select * from pg_logical_slot_get_changes('m',null,null);
ERROR:  replication slot "m" does not exist

This looks little weird as slot got dropped/removed internally . i guess it should get invalid rather than removed automatically.
Lets user's  delete the slot themself rather than automatically removed  as a surprise.

-- 
regards,tushar
EnterpriseDB  https://www.enterprisedb.com/
The Enterprise PostgreSQL Company