When do system events become effective?

Oracle 9.2.0.6, HP-UX 11.11

Hello world,
today I was trying to track down the SQL causing a full TEMP tablespace by tracing the 1652 event. I tried the following commands:

• ALTER SYSTEM SET EVENTS '1652 trace name errorstack';
• ALTER SYSTEM SET EVENTS = '1652 trace name errorstack';
• ALTER SYSTEM SET EVENTS = '1652 trace name context forever, level 12';
• oradebug event 1652 trace name errorstack

on a running system, but no trace files have been generated, although the alert log was flooded with this event after enabling trace.

I had the same effect with the 10046 event a while ago and supposed that it only comes in effect when a new session is started, but then "oradebug" would be usesless in this case. This cannot be. Unfortunately (as so often) I didn't have the time to research, but now i need some input from you folks!

So, why is there no tracefile after enabling trace and clearly seeing the traced event happen?

Regards,
Uwe

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