replication.go
func appendStats(peer string, start time.Time, logs float32) {
	metrics.MeasureSince([]string{"raft", "replication", "appendEntries", "rpc", peer}, start)
	metrics.IncrCounter([]string{"raft", "replication", "appendEntries", "logs", peer}, logs)
}
func appendStats(peer string, start time.Time, logs float32) {
	metrics.MeasureSince([]string{"raft", "replication", "appendEntries", "rpc", peer}, start)
	metrics.IncrCounter([]string{"raft", "replication", "appendEntries", "logs", peer}, logs)
}
// appendStats is used to emit stats about an AppendEntries invocation.