How to check if your physical standby database is applying logs or not

For Oracle versions 12.1 and lowe, use V$MANAGED_STANDBY:

SELECT CLIENT_PROCESS, PROCESS, THREAD#, SEQUENCE#, STATUS
FROM V$MANAGED_STANDBY
WHERE CLIENT_PROCESS='LGWR' OR PROCESS='MRP0'
;

CLIENT_PROCESS	PROCESS	THREAD#	SEQUENCE#	STATUS
LGWR	RFS	1	116713	RECEIVING
N/A	MRP0	1	114039	APPLYING_LOG

Important columns are

* PROCESS, which is the type of process whose information is being reported
MRP0 means the detached recovery server process. In this case, it is applying logs.

* CLIENT_PROCESS, which identifies the corresponding primary database process.
LGWR indicates the background log writer process

If there is a gap to be covered, you'll see the processes as being idle:

CLIENT_PROCESS	PROCESS	THREAD#	SEQUENCE#	STATUS
LGWR	RFS	1	116727	IDLE
N/A	MRP0	1	114115	WAIT_FOR_LOG

This is a good time to check where the gap is:

SELECT * FROM v$archive_gap;

THREAD#	LOW_SEQUENCE#	HIGH_SEQUENCE#	CON_ID
1	114120	114121	1

This matches the alert log of the standby database:

FAL[client]: Failed to request gap sequence
 GAP - thread 1 sequence 114120-114121

For Oracle 12.2 and beyond, Oracle encourage DBAs to use V$DATAGUARD_PROCESS (although V$MANAGED_STANDBY is still there for backward compability).
This view "displays one row for each Oracle Data Guard process that is currently running."

According to Oracle's documentation, there should be information about a process mapped toa role called "recovery logmerger" which in the ACTION column should state "APPLYING_LOG". I have repeatedly tried to find this information without luck.

What I do find in V$DATAGUARD_PROCESS is a role called "managed recovery".
If I run these queries against my database, they seem to yield two different results, the first telling me that manged recovery is idle, the second telling me that it is applying logs:

set lines 200
select name "process name",pid "standby server PID",role,action,client_role,client_pid "primary server PID" ,task_done
from v$dataguard_process
where role like 'managed recovery'
order by role desc, action;

SELECT CLIENT_PROCESS, PROCESS, THREAD#, SEQUENCE#, STATUS
FROM V$MANAGED_STANDBY
WHERE CLIENT_PROCESS='LGWR' OR PROCESS='MRP0';
exit

Output:

proce standby server PID       ROLE                    ACTION       CLIENT_ROLE      primary server PID T
----- ------------------------ ----------------------- ------------ ---------------- ------------------ -
MRP0  10714                    managed recovery        IDLE         none                              0 N


CLIENT_P PROCESS      THREAD#  SEQUENCE# STATUS
-------- --------- ---------- ---------- ------------
LGWR     RFS                1     116940 RECEIVING
N/A      MRP0               1     116940 APPLYING_LOG

Comments about this seemingly contradictory output would be much welcome.