Oracle - Symptoms of Output Post-processor (OPP) problem

1. Post-processing of request <request_id> failed at <date> <time> with the error message:
The Output Post-processor is running but has not picked up this request.
No further attempts will be made to post-process this request, and the request will be marked
with Warning status.
Setting the profile option Concurrent: OPP Response Timeout to a higher value may be necessary.

Solution: ask the Database Administrator(s) to have a look :-)

2. Beginning post-processing of request <request_id> on node <node> at <date> <time>.
Post-processing of request <request_id> failed at <date> <time> with the error message:
One or more post-processing actions failed. Consult the OPP service log for details.

OPP service log:
...Output file was found but is zero sized - Deleted
...java.lang.reflect.InvocationTargetException
...
...Caused by: java.lang.OutOfMemoryError: GC overhead limit exceeded

Possible Reason: too large output file.
Possible Solution: submit the request again with more specific parameters (e.g. smaller date range).