Warning: ORA-16857: standby disconnected from redo source for longer than specified threshold

One single 11.2.0.4 instance Oracle database alert log shows following information;

 RFS[1]: No standby redo logfiles available for thread 1

Data Guard shows ORA-16857 error:

DGMGRL> show database "TESTSTY";

Database - TESTSTY

Role: PHYSICAL STANDBY
 Intended State: APPLY-ON
 Transport Lag: 10 minutes 32 seconds (computed 48 seconds ago)
 Apply Lag: 10 minutes 32 seconds (computed 48 seconds ago)
 Apply Rate: 39.97 MByte/s
 Real Time Query: OFF
 Instance(s):
 TESTSTY

Database Warning(s):
 ORA-16857: standby disconnected from redo source for longer than 
specified threshold

Database Status:
WARNING

Checked both primary and standby database, the  standby online redo logs have been created. It is strange to see some of the thread id is different between primary and secondary database.

— on standby :

SQL> select GROUP#,THREAD#,BYTES/1024/1024 ,ARCHIVED,STATUS
       from v$standby_log; 2

GROUP#     THREAD#    BYTES/1024/1024 ARC STATUS
---------- ---------- --------------- --- ----------
 4         1          50              NO UNASSIGNED
 5         0          50              YES UNASSIGNED
 6         0          50              YES UNASSIGNED
 7         0          50              YES UNASSIGNED

— On Primary

SQL> select GROUP#,THREAD#,BYTES/1024/1024 ,ARCHIVED,STATUS 
       from v$standby_log;

GROUP#     THREAD#    BYTES/1024/1024 ARC STATUS
---------- ---------- --------------- --- ----------
 4         0          50              YES UNASSIGNED
 5         0          50              YES UNASSIGNED
 6         0          50              YES UNASSIGNED
 7         0          50              YES UNASSIGNED

Drop all standby online redo logs on both primary and standby databases, and recreate then again by specify “thread 1” explicitly.

-- for standby db which is under recovery, recovery needs to be stopped first
SQL>alter database recover managed standby database cancel;

SQL>alter database add standby logfile thread 1 group 4 size 50m;

It will create standby online redo logs for one under +FRA, and another one under from “db_create_file_dest” parameter, if “db_create_online_log_dest_x” are not defined.

Finally restart the recovery process, everything is fine.

SQL> ALTER DATABASE RECOVER MANAGED STANDBY DATABASE 
THROUGH ALL SWITCHOVER DISCONNECT USING CURRENT LOGFILE;

Database altered.