fix: Fix load slowly (#37454)

When there're a lot of loaded collections, they would occupy the target
observer scheduler’s pool. This prevents loading collections from
updating the current target in time, slowing down the load process.
This PR adds a separate target dispatcher for loading collections.

issue: https://github.com/milvus-io/milvus/issues/37166

---------

Signed-off-by: bigsheeper <yihao.dai@zilliz.com>

internal/querycoordv2/meta/target_manager.go

@@ -159,7 +159,6 @@ func (mgr *TargetManager) UpdateCollectionNextTarget(collectionID int64) error {
 	partitionIDs := lo.Map(partitions, func(partition *Partition, i int) int64 {
 		return partition.PartitionID
 	})
-	allocatedTarget := NewCollectionTarget(nil, nil, partitionIDs)
 
 	channelInfos := make(map[string][]*datapb.VchannelInfo)
 	segments := make(map[int64]*datapb.SegmentInfo, 0)
@@ -194,7 +193,8 @@ func (mgr *TargetManager) UpdateCollectionNextTarget(collectionID int64) error {
 		return nil
 	}
 
-	mgr.next.updateCollectionTarget(collectionID, NewCollectionTarget(segments, dmChannels, partitionIDs))
+	allocatedTarget := NewCollectionTarget(segments, dmChannels, partitionIDs)
+	mgr.next.updateCollectionTarget(collectionID, allocatedTarget)
 	log.Debug("finish to update next targets for collection",
 		zap.Int64("collectionID", collectionID),
 		zap.Int64s("PartitionIDs", partitionIDs),

internal/querycoordv2/observers/target_observer.go

@@ -87,8 +87,12 @@ type TargetObserver struct {
 	mut                  sync.Mutex                // Guard readyNotifiers
 	readyNotifiers       map[int64][]chan struct{} // CollectionID -> Notifiers
 
-	dispatcher *taskDispatcher[int64]
-	keylocks   *lock.KeyLock[int64]
+	// loadingDispatcher updates targets for collections that are loading (also collections without a current target).
+	loadingDispatcher *taskDispatcher[int64]
+	// loadedDispatcher updates targets for loaded collections.
+	loadedDispatcher *taskDispatcher[int64]
+
+	keylocks *lock.KeyLock[int64]
 
 	startOnce sync.Once
 	stopOnce  sync.Once
@@ -114,8 +118,8 @@ func NewTargetObserver(
 		keylocks:             lock.NewKeyLock[int64](),
 	}
 
-	dispatcher := newTaskDispatcher(result.check)
-	result.dispatcher = dispatcher
+	result.loadingDispatcher = newTaskDispatcher(result.check)
+	result.loadedDispatcher = newTaskDispatcher(result.check)
 	return result
 }
 
@@ -124,7 +128,8 @@ func (ob *TargetObserver) Start() {
 		ctx, cancel := context.WithCancel(context.Background())
 		ob.cancel = cancel
 
-		ob.dispatcher.Start()
+		ob.loadingDispatcher.Start()
+		ob.loadedDispatcher.Start()
 
 		ob.wg.Add(1)
 		go func() {
@@ -144,7 +149,8 @@ func (ob *TargetObserver) Stop() {
 		}
 		ob.wg.Wait()
 
-		ob.dispatcher.Stop()
+		ob.loadingDispatcher.Stop()
+		ob.loadedDispatcher.Stop()
 	})
 }
 
@@ -167,7 +173,13 @@ func (ob *TargetObserver) schedule(ctx context.Context) {
 
 		case <-ticker.C:
 			ob.clean()
-			ob.dispatcher.AddTask(ob.meta.GetAll()...)
+			loaded := lo.FilterMap(ob.meta.GetAllCollections(), func(collection *meta.Collection, _ int) (int64, bool) {
+				if collection.GetStatus() == querypb.LoadStatus_Loaded {
+					return collection.GetCollectionID(), true
+				}
+				return 0, false
+			})
+			ob.loadedDispatcher.AddTask(loaded...)
 
 		case req := <-ob.updateChan:
 			log.Info("manually trigger update target",
@@ -217,7 +229,7 @@ func (ob *TargetObserver) schedule(ctx context.Context) {
 func (ob *TargetObserver) Check(ctx context.Context, collectionID int64, partitionID int64) bool {
 	result := ob.targetMgr.IsCurrentTargetExist(collectionID, partitionID)
 	if !result {
-		ob.dispatcher.AddTask(collectionID)
+		ob.loadingDispatcher.AddTask(collectionID)
 	}
 	return result
 }

internal/querycoordv2/observers/target_observer_test.go

@@ -90,7 +90,9 @@ func (suite *TargetObserverSuite) SetupTest() {
 	suite.collectionID = int64(1000)
 	suite.partitionID = int64(100)
 
-	err = suite.meta.CollectionManager.PutCollection(utils.CreateTestCollection(suite.collectionID, 1))
+	testCollection := utils.CreateTestCollection(suite.collectionID, 1)
+	testCollection.Status = querypb.LoadStatus_Loaded
+	err = suite.meta.CollectionManager.PutCollection(testCollection)
 	suite.NoError(err)
 	err = suite.meta.CollectionManager.PutPartition(utils.CreateTestPartition(suite.collectionID, suite.partitionID))
 	suite.NoError(err)
@@ -302,7 +304,8 @@ func (suite *TargetObserverCheckSuite) SetupTest() {
 func (s *TargetObserverCheckSuite) TestCheck() {
 	r := s.observer.Check(context.Background(), s.collectionID, common.AllPartitionsID)
 	s.False(r)
-	s.True(s.observer.dispatcher.tasks.Contain(s.collectionID))
+	s.False(s.observer.loadedDispatcher.tasks.Contain(s.collectionID))
+	s.True(s.observer.loadingDispatcher.tasks.Contain(s.collectionID))
 }
 
 func TestTargetObserver(t *testing.T) {