ORA-19909: datafile 1 belongs to an orphan incarnation

Error: On starting the MRP service on the standby database, it does not work. I got the following error in the alert log file:

The managed recovery process (MRP) will maintain and apply the archive redo logs information to the standby database.

ORA-19909: datafile 1 belongs to an orphan incarnation
ORA-01110: data file 1: '/u02/oradata/ORCL/system01.dbf'
Completed: alter database recover managed standby database disconnect from session
Mon Oct 19 10:43:51 2023
MRP0: Background Media Recovery process shutdown (ORCL)

Cause: Standby and primary database using different incarnation

Solution: We need to reset the incarnation of Standby so that it will match with the primary and our MRP service will start.

Check the primary incarnation value

--Check the incarnation value on Primary
rman target /@PRIM

RMAN> list incarnation of database;
using target database control file instead of recovery catalog

List of Database Incarnations
DB Key Inc Key DB Name DB ID      STATUS  Reset SCN Reset Time
------ ------- ------- ---------- ------- ---------
 ----------
1      1       ORCL    2980942556 PARENT  1         30-JAN-2023 11:31:04

2      2       ORCL    2980942556 CURRENT 2344346   11-AUG-2023 03:02:53

Check the Standby incarnation values

--Check the incarnation value on Primary
rman target /@Standby

RMAN> list incarnation of database;
using target database control file instead of recovery catalog

List of Database Incarnations
DB Key Inc Key DB Name DB ID      STATUS  Reset SCN Reset Time
------ ------- ------- ---------- ------- --------- ----------
1      1       ORCL    2980942556 PARENT  1         30-JAN-2023 11:31:44
2      2       ORCL    2980942556 PARENT  2344346   11-AUG-2023 03:32:23
3      3       ORCL    2980942556 CURRENT 4635321   15-AUG-2023 06:14:33

As shown incarnation is not the same for both databases, you can change the current incarnation to 2 for standby so that it will match with the primary database.

Reset the incarnation on standby database

RMAN>reset database to incarnation 2;
database reset to incarnation 2
RMAN> list incarnation of database;

using target database control file instead of recovery catalog

List of Database Incarnations
DB Key Inc Key DB Name DB ID      STATUS  Reset SCN Reset Time
------ ------- ------- ---------- ------- --------- ----------
1      1       ORCL    2980942556 PARENT  1         30-JAN-2023 11:31:44
2      2       ORCL    2980942556 CURRENT 2344346   11-AUG-2023 03:32:23
3      3       ORCL    2980942556 ORPHAN  4635321   15-AUG-2023 06:14:33

Start the MRP service on the standby database hopefully, it will fix the issue.

sqlplus sys@standby as sysdba

SQL> alter database recover managed standby database disconnect from session;