raft/progress.go
func (pr *Progress) maybeUpdate(n uint64) bool {
	var updated bool
	if pr.Match < n {
		pr.Match = n
		updated = true
		pr.resume()
	}
	if pr.Next < n+1 {
		pr.Next = n + 1
	}
	return updated
}
func (pr *Progress) maybeUpdate(n uint64) bool {
	var updated bool
	if pr.Match < n {
		pr.Match = n
		updated = true
		pr.resume()
	}
	if pr.Next < n+1 {
		pr.Next = n + 1
	}
	return updated
}
// maybeUpdate returns false if the given n index comes from an outdated message.
// Otherwise it updates the progress and returns true.