Hello Sander,
Can you post the explain plan output of these queries?
> SELECT * FROM events_events LEFT OUTER JOIN events_event_types ON
> eventType_id=events_event_types.id WHERE severity=20 AND (eventType_id
> IN (71)) ORDER BY datetime DESC limit 50;
>
> SELECT * FROM events_events LEFT OUTER JOIN events_event_types ON
> eventType_id=events_event_types.id WHERE severity=70 AND (eventType_id
> IN (71, 999)) ORDER BY datetime DESC LIMIT 50;
>
regards
Yeb Havinga