Ben Darnell 2e1c36cdd9 raft: introduce MsgHeartbeatResp.
Now that heartbeats are distinct from MsgApp{,Resp}, the retries
currently performed in stepLeader's MsgAppResp section are only
performed on an actual MsgAppResp (or a new MsgProp). This means
that it may take a long time to recover from a dropped MsgAppResp
in a quiet cluster.

This commit adds a dedicated heartbeat response message. This message
does not convey the follower's current log position because the
MsgHeartbeat does not include the leaders term and index. Upon receipt
of a heartbeat response, the leader may retry the latest MsgApp if it
believes the follower to be behind.
2015-01-14 17:34:10 -05:00
..
2015-01-14 17:34:10 -05:00
2015-01-14 17:34:10 -05:00