Heartbeats are issued periodically by QMF agents. Each heartbeat is stateless - there is no information loss if a heartbeat is dropped or ignored by the client. While performance testing, it was discovered that multiple heartbeats will queue up should a console be unable to consume them fast enough. Most of these heartbeats are stale: the agent has issue a new heartbeat(s) since the older heartbeat was queued. Processing these "stale" heartbeats is useless.
By setting the TTL in heartbeat messages, stale heartbeats will be discarded by the broker instead of being sent to the console.