We see a MaybeEncodingError raised from billboard when trying to unpickle our custom exception classes.

MaybeEncodingError: Error sending result: ''(1, <ExceptionInfo: TrinoStatementExecError()>, None)''. Reason: ''PicklingError("Can\'t pickle <class \'koku.trino_database.TrinoStatementExecError\'>: it\'s not the same object as koku.trino_database.TrinoStatementExecError")''.
  File "billiard/pool.py", line 366, in workloop
    put((READY, (job, i, result, inqW_fd)))
  File "billiard/queues.py", line 366, in put
    self.send_payload(ForkingPickler.dumps(obj))
  File "billiard/reduction.py", line 56, in dumps
    cls(buf, protocol).dump(obj)

This seems to only happen on custom exception classes that accept parameters. As an example, this has long happened with ExtendedDeadlockDetected but only recently started happening with TrinoStatementExecError after I changed it to accept arguments.

Extensive research on this PicklingError returns many inconclusive recommendations, some of which are outdated.

The current plan is to add a _reduce_ method to our custom exception classes to give deterministic unpicking of the objects.