Heartbeats

The heartbeat mechanism is used to periodically check the state of the host server. They are sent, by default, every 15 seconds. Heartbeats are only sent when the link has been idle for 15 seconds. If other requests have been sent and acknowledged, heartbeats won’t be sent.

If the router doesn’t see the reply in time, it will retry heartbeats (at a smaller interval) until either they succeed, or the connection is declared dead.

The router will treat a query timeout also as a failed heartbeat and begin the heartbeat retry operation.