Oracle: ORA-12154: Cannot connect to database... error on Service

Hi yaman123,

Since the ORA-12154 errors started occurring right after the September update and there were no configuration changes, it’s possible that the update introduced a bug. Please submit a Microsoft support ticket so they can look into this and help resolve the issue.

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Thank you.

Hi yaman123,

The official documentation states that the ORA-12154 error happens when the Oracle alias can't be resolved, often because tnsnames.ora is missing or set up incorrectly. It recommends confirming that the 64-bit Oracle Client for Microsoft Tools (OCMT) is installed on the Gateway machine and that the alias is properly configured in tnsnames.ora. The documentation also suggests testing the connection through Power BI Desktop on the Gateway machine to make sure everything is set up correctly.

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Thank you.

Hi yaman123, 

I’d build on what’s already in the thread with two points:

1) ORA-12154 in the Service almost always means the gateway machine can’t resolve your Oracle connect identifier.

2) the September Desktop bug people are seeing is real, but Desktop and the Service take different paths. Desktop uses the PC you’re on; the Service uses the on-premises data gateway and whatever Oracle client and environment that server has.

Here's some troubleshooting steps:

1. Bypass TNS and test Easy Connect
   Edit the Oracle data source in the Service and set Server to this format:
   host:port/service_name
   Example: db01.yourcorp.local:1521/SALES. If Test Connection succeeds, your TNS name resolution on the gateway is the culprit. Docs: Power Query Oracle connector and Oracle’s Easy Connect syntax here.
2. Check if your gateway updated
   Many orgs update the gateway monthly. If your issue began recently, that can align with an update or a service restart that dropped environment variables. Check the gateway version and consider testing July or August 2025 on a spare node or rollback if needed (supported versions and downloads are listed here): gateway monthly updates.
3. Reassert TNS on the gateway server
   On the gateway box, set a system environment variable TNS_ADMIN to the folder with tnsnames.ora and sqlnet.ora, ensure the gateway service account can read it, then restart the “On-premises data gateway” Windows service. Guide: Manage your Oracle data source via gateway.
4. Prove it from the gateway as the service account
   On the gateway host, run tnsping <your_alias> and connect with SQL*Plus or SQL Developer using that alias. If tnsping fails, ORA-12154 is expected. Oracle’s definition of 12154 is clear that it’s a name resolution problem: Oracle ORA-12154.
5. Rebind and test in the Service
   In the dataset settings, bind to the validated gateway data source and hit Test Connection. Reference: gateway binding steps.

If you confirm Easy Connect works in the Service, I’d leave it in place and circle back to TNS later. If neither Easy Connect nor TNS works and you’ve validated firewall and listener, I’d open a Microsoft ticket and include gateway version, Oracle client version, TNS_ADMIN path, the exact Server value you used, and tnsping output from the gateway host.

If you found this helpful, consider giving some Kudos. If I answered your question or solved your problem, mark this post as the solution.

Another post on a separate thread mentioned that everything works if you go back to the July upgrade so it's fairly evident that the September update broke it.

This is an update/workaround from Microsoft regarding the issue