Thin client error: DPY-6000: cannot connect to database. Listener refused connection. (Similar to ORA-12660)

[harri-pasanen]

1. What versions are you using?

python-oracledb 1.0.3
Oracle Database 19c Enterprise Edition Release 19.0.0.0.0
platform.platform: Linux-3.10.0-1160.71.1.el7.x86_64-x86_64-with-glibc2.17
platform.python_version: 3.9.6
sys.maxsize > 2**32: True

2. Is it an error or a hang or a crash?

Connection fails to Exadata RAC with the thin client.

connection = oracledb.connect(user=admin, password=args.adminpwd,
dsn=args.service_name, config_dir = tnsdir)

3. What error(s) or behavior you are seeing?

With thin client connection to a single instance non RAC db seems to work fine.
But I cannot connect to Exadata RAC instance with thin client, it causes the exception:

oracledb.exceptions.OperationalError: DPY-6000: cannot connect to database. Listener refused connection. (Similar to ORA-12660)

Problem tns entry is like:
x01 =
(DESCRIPTION =
(ADDRESS_LIST =
(FAILOVER = ON)
(LOAD_BALANCE = ON)
(ADDRESS = (PROTOCOL = TCP)(HOST = xt01dev-scan.home.net)(PORT = 1521))
(ADDRESS = (PROTOCOL = TCP)(HOST = xt02dev-scan.home.net)(PORT = 1521))
)
(CONNECT_DATA =
(SERVER = DEDICATED)
(SERVICE_NAME = dbox_svc.tst.tns)
)
)

if I call init_oracle_client() it starts working.

5. Does your application call init_oracle_client()?

No.

But if I call init_oracle_client(), it starts working.

6. Include a runnable Python script that shows the problem.

# Uncomment below line and the problem goes away
# oracledb.init_oracle_client()  
connection = oracledb.connect(user=admin, password=args.adminpwd, 
                                dsn=args.service_name, config_dir = tnsdir)

[harri-pasanen]

Note that I tried pretty much all connection modes, including those not using tnsnames.ora, but could not make a connection to this particular db with the thin client. Thick client works fine.

[anthony-tuininga]

This is a known limitation of the thin driver as can be seen in the documentation. The only solution (if you want to use thin mode) is to make the native network encryption and checksumming not mandatory; otherwise, you will have to use thick mode. You can make this an enhancement request if you'd like, but I'm not sure where the priority would be as we have a long list of enhancement requests for thin mode!

[bassg0navy]

This thread helped a lot 👍 and saved an unnecessary issue being opened.

[cjbj]

Closing. We have NNE support on our 'todo' list.