I configured logical replication for PostgreSQL 10.4 on 2 machines, set wal_level to logical, created a publication on master node and created a subscription on standby node according to the PostgreSQL documentation. Could you please suggest an approach for replication state monitoring.
According to my experience the monitoring of pg_stat_subscription and pg_publication, pg_replication_slots unfortunately is not enough for this aim. Moreover standby database does not prohibit write operations by default and it can lead to some inconsistency between these databases.
For example a chain of queries as SELECT pg_is_is_recovery(), SELECT * FROM pg_stat_replication and SELECT * FROM pg_stat_wal_receiver provide insight into replication state for hot_standby replication.
So is there a reliable way of replication state monitoring for logical replication?