At work, we are currently migrating to Oracle. Quite a learning curve… We experienced interruptions in the service from the TNS-listener, and the JDBC driver would return

ORA-12519, TNS:no appropriate service handler found

Poking around the Oracle installation, I noticed that the file /oracle/diag/tnslsnr/ora-dev/listener/trace/listener.log contained a lot of:

WARNING: Subscription for node down event still pending

Digging deeper, I found this page. So I added the line:

SUBSCRIBE_FOR_NODE_DOWN_EVENT_Listener=OFF

to the listener.ora and now it seems that our TNS-listener is behaving nicely