A review on v62-006: failover-ready validation steps doc -
+ Next, check that the logical replication slots identified above exist on
+ the standby server. This step can be skipped if
+ <varname>standby_slot_names</varname> has been correctly configured.
+<programlisting>
+test_standby=# SELECT bool_and(synced AND NOT temporary AND
conflict_reason IS NULL) AS failover_ready
+ FROM pg_replication_slots
+ WHERE slot_name in ('sub');
+ failover_ready
+----------------
+ t
+(1 row)
This query does not ensure that all the logical replication slots
exist on standby. Due to the 'IN ('slots')' check, it will return
'true' even if only one or a few slots exist.