I googled a lot regarding the error message “password is not set” when testing a datasource in WebSphere (126.96.36.199), but I did not find a solution. A co-worker finally found a solution (by accident?).
While having the application JVMs running, I created a new JAAS-J2C authenticator (in my case the same login but a different password), and changed the datasource to use the new authenticator. I saved the config and synchronized it. The files config/cells/cellname/nodes/nodename/resources.xml and config/cells/cellname/security.xml showed that the changes arrived on the node. Testing the datasource connectivity fails now with:
DSRA8201W: DataSource Configuration: DSRA8040I: Failed to connect to the DataSource. Encountered java.sql.SQLException: The application server rejected the connection. (Password is not set.)DSRA0010E: SQL State = 08004, Error Code = ‑99,999.
Restarting the application JVMs does not help.
After stopping everything (application JVMs, nodeagent and deployment manager) and starting everything again, the connection test of the datasource works directly as expected.
I have not tested if it is enough to just stop all application JVMs on one node and the correspding nodeagent, or if I really have to stop the deployment manager too.