Steps to convert 12c Physical Standby Database to Active Data Guard.

Physical Standby Database had already been created and Data Guard Broker configuration exists before.

Step 1: Stop the MRP Process on the Standby Database. You can connect to DGMGRL Utility from either Primary Database Server or Standby Database Server.

DGMGRL> connect sys/xxxxxxxx
Connected as SYSDG.
DGMGRL> EDIT DATABASE "MY12CDBSTBY" SET STATE='APPLY-OFF';
Succeeded.
DGMGRL> exit

Step 2: Verify that the Physical Standby Database is in MOUNTED Stage as it is expected to be.

SQL> SELECT name,open_mode,database_role,cdb FROM v$database;

NAME      OPEN_MODE            DATABASE_ROLE    CDB
--------- -------------------- ---------------- ---
MY12CDB   MOUNTED              PHYSICAL STANDBY YES

SQL> SELECT name,open_mode FROM v$pdbs;

NAME                           OPEN_MODE
------------------------------ ----------
PDB$SEED                       MOUNTED
MYPDB1                         MOUNTED
MYPDB2                         MOUNTED

Step 3: Open the Physical Standby Database in Read Only Mode.

SQL> ALTER DATABASE OPEN READ ONLY;

Database altered.

Step 4: Now check the status of the Pluggable Databases.

SQL> SELECT name,open_mode,database_role,cdb FROM v$database;

NAME      OPEN_MODE            DATABASE_ROLE    CDB
--------- -------------------- ---------------- ---
MY12CDB   READ ONLY            PHYSICAL STANDBY YES

SQL> SELECT name,open_mode FROM v$pdbs;

NAME                           OPEN_MODE
------------------------------ ----------
PDB$SEED                       READ ONLY
MYPDB1                         MOUNTED
MYPDB2                         MOUNTED

Step 5: Open the Pluggable Databases in READ ONLY Mode.

SQL> ALTER PLUGGABLE DATABASE ALL OPEN READ ONLY;

Pluggable database altered.
SQL> SELECT name,open_mode,database_role,cdb FROM v$database;

NAME      OPEN_MODE            DATABASE_ROLE    CDB
--------- -------------------- ---------------- ---
MY12CDB   READ ONLY            PHYSICAL STANDBY YES

SQL> SELECT name,open_mode FROM v$pdbs;

NAME                           OPEN_MODE
------------------------------ ----------
PDB$SEED                       READ ONLY
MYPDB1                         READ ONLY
MYPDB2                         READ ONLY

SQL>

Step 6: Now Start the MRP Process on the Physical Standby Database.

DGMGRL> connect sys/xxxxxxx
Connected as SYSDG.
DGMGRL> EDIT DATABASE "MY12CDBSTBY" SET STATE='APPLY-ON';
Succeeded.

Step 7: Verify that the Primary Database and Standby Database are in SYNC.

DGMGRL> show database "MY12CDBSTBY";

Database - MY12CDBSTBY

  Role:               PHYSICAL STANDBY
  Intended State:     APPLY-ON
  Transport Lag:      0 seconds (computed 0 seconds ago)
  Apply Lag:          0 seconds (computed 0 seconds ago)
  Average Apply Rate: 5.00 KByte/s
  Real Time Query:    ON
  Instance(s):
    my12cdb

Database Status:
SUCCESS

DGMGRL>