I am seeing sporadic reports of an application failing certain queries with an "End of TNS data channel" error from the Oracle (10g) server. Are there any queries I can run (e.g., with SQL*Plus or other tool) to ask the Oracle server what was the cause of such failures? What logs should I look for?
You will probably need to get in touch with Oracle support. Making sure you have the latest patch set applied for your version may help - or finding the exact SQL executing when the server process crashed and working around the Oracle bug causing the crash is often possible.