MultitenantQueue.delete method to return boolean value indicating whether deleted message did exist in queue or not. If processing of dequeued message takes more time than defined invisibility period then same message can be dequeued again after invisibility period has passed. This can result to situation where multiple workers read same message and try to delete it after processing. If deleted message does not exist it indicates that it was dequeued and deleted already before meaning that invisibility period might be too short.