[#1449] tree: Add ApplyBatch method

Concurrent Apply can lead to child node applies before parent, so
undo/redo operations will perform. This leads to performance degradation
in case of tree with many sublevels.

Signed-off-by: Dmitrii Stepanov <d.stepanov@yadro.com>

pkg/services/tree/sync.go

@@ -177,37 +177,29 @@ func mergeOperationStreams(streams []chan *pilorama.Move, merged chan<- *piloram
 func (s *Service) applyOperationStream(ctx context.Context, cid cid.ID, treeID string,
 	operationStream <-chan *pilorama.Move,
 ) uint64 {
-	errGroup, _ := errgroup.WithContext(ctx)
-	const workersCount = 1024
-	errGroup.SetLimit(workersCount)
-
-	// We run TreeApply concurrently for the operation batch. Let's consider two operations
-	// in the batch m1 and m2 such that m1.Time < m2.Time. The engine may apply m2 and fail
-	// on m1. That means the service must start sync from m1.Time in the next iteration and
-	// this height is stored in unappliedOperationHeight.
-	var unappliedOperationHeight uint64 = math.MaxUint64
-	var heightMtx sync.Mutex
-
 	var prev *pilorama.Move
+	var batch []*pilorama.Move
 	for m := range operationStream {
 		// skip already applied op
 		if prev != nil && prev.Time == m.Time {
 			continue
 		}
 		prev = m
+		batch = append(batch, m)
 
-		errGroup.Go(func() error {
-			if err := s.forest.TreeApply(ctx, cid, treeID, m, true); err != nil {
-				heightMtx.Lock()
-				unappliedOperationHeight = min(unappliedOperationHeight, m.Time)
-				heightMtx.Unlock()
-				return err
+		if len(batch) == s.syncBatchSize {
+			if err := s.forest.TreeApplyBatch(ctx, cid, treeID, batch); err != nil {
+				return batch[0].Time
 			}
-			return nil
-		})
+			batch = batch[:0]
+		}
 	}
-	_ = errGroup.Wait()
-	return unappliedOperationHeight
+	if len(batch) > 0 {
+		if err := s.forest.TreeApplyBatch(ctx, cid, treeID, batch); err != nil {
+			return batch[0].Time
+		}
+	}
+	return math.MaxUint64
 }
 
 func (s *Service) startStream(ctx context.Context, cid cid.ID, treeID string,