p2p: simpler priority queue (backport #8929) (#8956)

internal/p2p/pqueue.go

@@ -29,8 +29,16 @@ func (pq priorityQueue) get(i int) *pqEnvelope { return pq[i] }
 func (pq priorityQueue) Len() int              { return len(pq) }
 
 func (pq priorityQueue) Less(i, j int) bool {
-	// if both elements have the same priority, prioritize based on most recent
+	// if both elements have the same priority, prioritize based
+	// on most recent and largest
 	if pq[i].priority == pq[j].priority {
+		diff := pq[i].timestamp.Sub(pq[j].timestamp)
+		if diff < 0 {
+			diff *= -1
+		}
+		if diff < 10*time.Millisecond {
+			return pq[i].size > pq[j].size
+		}
 		return pq[i].timestamp.After(pq[j].timestamp)
 	}
 
@@ -272,12 +280,10 @@ func (s *pqScheduler) process() {
 }
 
 func (s *pqScheduler) push(pqEnv *pqEnvelope) {
-	chIDStr := strconv.Itoa(int(pqEnv.envelope.channelID))
-
 	// enqueue the incoming Envelope
 	heap.Push(s.pq, pqEnv)
 	s.size += pqEnv.size
-	s.metrics.PeerQueueMsgSize.With("ch_id", chIDStr).Add(float64(pqEnv.size))
+	s.metrics.PeerQueueMsgSize.With("ch_id", strconv.Itoa(int(pqEnv.envelope.channelID))).Add(float64(pqEnv.size))
 
 	// Update the cumulative sizes by adding the Envelope's size to every
 	// priority less than or equal to it.