Re: Minimal logical decoding on standbys

On Thu, 4 Jul 2019 at 17:21, Amit Khandekar <amitdkhan(dot)pg(at)gmail(dot)com> wrote:
>
> On Thu, 4 Jul 2019 at 15:52, tushar <tushar(dot)ahuja(at)enterprisedb(dot)com> wrote:
> >
> > 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)
>
> Which specific problem are you referring to ? Removing a conflicting
> slot, itself is the part of the fix for the conflicting slot problem.
>
> >
> > 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.
>
> It was earlier discussed about what action should be taken when we
> find conflicting slots. Out of the options, one was to drop the slot,
> and we chose that because that was simple. See this :
> https://www.postgresql.org/message-id/flat/20181212204154.nsxf3gzqv3gesl32%40alap3.anarazel.de

Sorry, the above link is not the one I wanted to refer to. Correct one is this :

https://www.postgresql.org/message-id/20181214005521.jaty2d24lz4nroil%40alap3.anarazel.de

--
Thanks,
-Amit Khandekar
EnterpriseDB Corporation
The Postgres Database Company