Gracefully handle 'database is locked' error on flush

This might happen on high event load and is not that critical
as the database items were already transmitted and are marked as sent.
The events will be removed from the database on the next run.

Author: eht16

logstash_async/worker.py

@@ -180,9 +180,16 @@ def _flush_queued_events(self, force=False):
                 self._safe_log(u'exception', u'An error occurred while sending events: %s', e)
                 self._database.requeue_queued_events(queued_events)
             else:
-                self._database.delete_queued_events()
+                self._delete_queued_events_from_database()
                 self._reset_flush_counters()
 
+    # ----------------------------------------------------------------------
+    def _delete_queued_events_from_database(self):
+        try:
+            self._database.delete_queued_events()
+        except DatabaseLockedError:
+            pass  # nothing to handle, if it fails, we delete those events in a later run
+
     # ----------------------------------------------------------------------
     def _queued_event_interval_reached(self):
         delta = datetime.now() - self._last_event_flush_date