Re: Minimal logical decoding on standbys

On 07/01/2019 11:04 AM, Amit Khandekar wrote:
> 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
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