try to reuse the info.Queue conversion has a negative performance effect

txn/flusher.go

@@ -159,33 +159,41 @@ const preloadBatchSize = 100
 
 func (f *flusher) recurse(t *transaction, seen map[bson.ObjectId]*transaction, preloaded map[bson.ObjectId]*transaction) error {
 	seen[t.Id] = t
+	// we shouldn't need this one anymore because we are processing it now
 	delete(preloaded, t.Id)
 	err := f.advance(t, nil, false)
 	if err != errPreReqs {
 		return err
 	}
+	toPreload := make([]bson.ObjectId, 0)
 	for _, dkey := range t.docKeys() {
-		remaining := make([]bson.ObjectId, 0, len(f.queue[dkey]))
-		toPreload := make(map[bson.ObjectId]struct{}, len(f.queue[dkey]))
+		queue := f.queue[dkey]
+		remaining := make([]bson.ObjectId, 0, len(queue))
 		for _, dtt := range f.queue[dkey] {
 			id := dtt.id()
-			if _, scheduled := toPreload[id]; seen[id] != nil || scheduled || preloaded[id] != nil {
+			if seen[id] != nil {
 				continue
 			}
-			toPreload[id] = struct{}{}
 			remaining = append(remaining, id)
 		}
-		// done with this map
-		toPreload = nil
+
 		for len(remaining) > 0 {
-			batch := remaining
-			if len(batch) > preloadBatchSize {
-				batch = remaining[:preloadBatchSize]
+			toPreload = toPreload[:0]
+			batchSize := preloadBatchSize
+			if batchSize > len(remaining) {
+				batchSize = len(remaining)
 			}
-			remaining = remaining[len(batch):]
-			err := f.loadMulti(batch, preloaded)
-			if err != nil {
-				return err
+			batch := remaining[:batchSize]
+			remaining = remaining[batchSize:]
+			for _, id := range batch {
+				if preloaded[id] == nil {
+					toPreload = append(toPreload, id)
+				}
+			}
+			if len(toPreload) > 0 {
+				if err := f.loadMulti(toPreload, preloaded); err != nil {
+					return err
+				}
 			}
 			for _, id := range batch {
 				if seen[id] != nil {
@@ -302,6 +310,8 @@ NextDoc:
 			if info.Remove == "" {
 				// Fast path, unless workload is insert/remove heavy.
 				revno[dkey] = info.Revno
+				// We updated the Q, so this should force refresh
+				// TODO: We could *just* add the new txn-queue entry/reuse existing tokens
 				f.queue[dkey] = tokensWithIds(info.Queue)
 				f.debugf("[A] Prepared document %v with revno %d and queue: %v", dkey, info.Revno, info.Queue)
 				continue NextDoc
@@ -363,8 +373,14 @@ NextDoc:
 				} else {
 					f.debugf("[B] Prepared document %v with revno %d and queue: %v", dkey, info.Revno, info.Queue)
 				}
-				revno[dkey] = info.Revno
-				f.queue[dkey] = tokensWithIds(info.Queue)
+				existRevno, rok := revno[dkey]
+				existQ, qok := f.queue[dkey]
+				if rok && qok && existRevno == info.Revno && len(existQ) == len(info.Queue) {
+					// We've already loaded this doc, no need to load it again
+				} else {
+					revno[dkey] = info.Revno
+					f.queue[dkey] = tokensWithIds(info.Queue)
+				}
 				continue NextDoc
 			}
 		}
@@ -498,15 +514,25 @@ func (f *flusher) rescan(t *transaction, force bool) (revnos []int64, err error)
 			goto RetryDoc
 		}
 		revno[dkey] = info.Revno
-
+		// TODO(jam): 2017-05-31: linear search for each token in info.Queue during all rescans is potentially O(N^2)
+		// if we first checked to see that we've already loaded this info.Queue in f.queue, we could use a different
+		// structure (map) to do faster lookups to see if the tokens are already present.
 		found := false
 		for _, id := range info.Queue {
 			if id == tt {
 				found = true
 				break
 			}
 		}
-		f.queue[dkey] = tokensWithIds(info.Queue)
+		// f.queue[dkey] = tokensWithIds(info.Queue, &RescanUpdatedQueue)
+		existQ, qok := f.queue[dkey]
+		if qok && len(existQ) == len(info.Queue) {
+			// we could check that info.Q matches existQ.tt
+		} else {
+			if len(existQ) != len(info.Queue) {
+			}
+			f.queue[dkey] = tokensWithIds(info.Queue)
+		}
 		if !found {
 			// Rescanned transaction id was not in the queue. This could mean one
 			// of three things:

txn/txn.go

@@ -136,8 +136,10 @@ func newNonce() string {
 
 type token string
 
-func (tt token) id() bson.ObjectId { return bson.ObjectIdHex(string(tt[:24])) }
-func (tt token) nonce() string     { return string(tt[25:]) }
+func (tt token) id() bson.ObjectId {
+	return bson.ObjectIdHex(string(tt[:24]))
+}
+func (tt token) nonce() string { return string(tt[25:]) }
 
 // Op represents an operation to a single document that may be
 // applied as part of a transaction with other operations.
@@ -330,6 +332,8 @@ func (r *Runner) ResumeAll() (err error) {
 			panic(fmt.Errorf("invalid state for %s after flush: %q", &t, t.State))
 		}
 	}
+	// TODO(jam): 2017-06-04 This is not calling iter.Close() and dealing with
+	// any error it might encounter (db connection closed, etc.)
 	return nil
 }
 
@@ -478,7 +482,6 @@ func (r *Runner) loadMulti(ids []bson.ObjectId, preloaded map[bson.ObjectId]*tra
 	return nil
 }
 
-
 type typeNature int
 
 const (