On one of our databases, we're missing the queue SYS$SERVICE_METRICS (as seen in dba_queues on other databases) and its table SYS$SERVICE_METRICS_TAB (as seen in dba_tables). I searched for ORA-25205 ("the QUEUE %s.%s does not exist") and easily found documents on how to recreate various queues. But I found nobody either here on MyOracleSupport or the Internet that explains why this or some other queue would disappear. Obviously we never messed with the data dictionary of this database. It's reasonable to assume nobody having this problem did. So, what caused an AQ to disappear? Problematic patching (which we do every 3 months)? But we patched the databases without any error. Or kill'ed -9 a data pump process (yes we sometimes do that in a hurry), but that should, if it does at all, cause a problem to a queue named like %KUPC$DATAPUMP%. This SYS$SERVICE_METRICS queue is related to services. We never had issues with services on this database. So, can anybody guess at a cause why a queue is gone so we can prevent it from happening again? (The database we're missing the queue in is 18c, Exadata. And we never use advanced queueing, except implicitly by tools such as data pump or DBMS scheduler.)