In my parameter files for both primary and standby I have service_names both different for primary and standby consider as prod for primary and stnby for standby database. So which service_name I should give in your myapp entry mentioned below

MYAPP =
(DESCRIPTION =
(ADDRESS_LIST =
(ADDRESS = (PROTOCOL = TCP)(HOST = HostA)(PORT = 1521))
(ADDRESS = (PROTOCOL = TCP)(HOST = HostB)(PORT = 1521))
)
(CONNECT_DATA =
(SERVICE_NAME = myapp)
)
)

only db_name is common for me in both parameter files i.e. prod.

from primary

*.db_name=’prod’
*.db_unique_name=’prod’
*.service_names=’prod’
*.instance_name=’prod’

from physical standby

*.db_name=’prod’
*.db_unique_name=’stnby’
*.service_names=’stnby’
*.instance_name=’stnby’

Also listeners on both Primary and Standby hosts are having different SIDs i.e prod and stnby

from primary

(SID_DESC =
(GLOBAL_DBNAME = prod)
(ORACLE_HOME = /u01/oradha/product/11.2.0)
(SID_NAME = prod)
)
————————————————————————–
from physical standby

(SID_DESC =
(GLOBAL_DBNAME = stnby)
(ORACLE_HOME = /u01/oradha/product/11.2.0)
(SID_NAME = stnby)
)

Please clarify what tnsentry we need to use for seamless connection to database which may be Primary or Physical Standby.

Regards,
Mujib Dave