Make querynode LoadSegments interface idempotent (#17109)

This PR makes the following changes:
* separate LoadSegmentsTask into two phases: PreExecute and Execute
* filters out segments that are already loaded in PreExecute phase

Signed-off-by: Letian Jiang <letian.jiang@zilliz.com>

internal/querynode/task.go

@@ -633,14 +633,8 @@ func (l *loadSegmentsTask) OnEnqueue() error {
 }
 
 func (l *loadSegmentsTask) PreExecute(ctx context.Context) error {
-	return nil
-}
-
-func (l *loadSegmentsTask) Execute(ctx context.Context) error {
-	// TODO: support db
-	log.Info("LoadSegment start", zap.Int64("msgID", l.req.Base.MsgID))
+	log.Info("LoadSegmentTask PreExecute start", zap.Int64("msgID", l.req.Base.MsgID))
 	var err error
-
 	// init meta
 	collectionID := l.req.GetCollectionID()
 	l.node.historical.replica.addCollection(collectionID, l.req.GetSchema())
@@ -656,13 +650,29 @@ func (l *loadSegmentsTask) Execute(ctx context.Context) error {
 		}
 	}
 
-	err = l.node.loader.loadSegment(l.req, segmentTypeSealed)
+	// filter segments that are already loaded in this querynode
+	var filteredInfos []*queryPb.SegmentLoadInfo
+	for _, info := range l.req.Infos {
+		if !l.node.historical.replica.hasSegment(info.SegmentID) {
+			filteredInfos = append(filteredInfos, info)
+		} else {
+			log.Debug("ignore segment that is already loaded", zap.Int64("segmentID", info.SegmentID))
+		}
+	}
+	l.req.Infos = filteredInfos
+	log.Info("LoadSegmentTask PreExecute done", zap.Int64("msgID", l.req.Base.MsgID))
+	return nil
+}
+
+func (l *loadSegmentsTask) Execute(ctx context.Context) error {
+	// TODO: support db
+	log.Info("LoadSegmentTask Execute start", zap.Int64("msgID", l.req.Base.MsgID))
+	err := l.node.loader.loadSegment(l.req, segmentTypeSealed)
 	if err != nil {
 		log.Warn(err.Error())
 		return err
 	}
-
-	log.Info("LoadSegments done", zap.Int64("msgID", l.req.Base.MsgID))
+	log.Info("LoadSegmentTask Execute done", zap.Int64("msgID", l.req.Base.MsgID))
 	return nil
 }
 

internal/querynode/task_test.go

@@ -574,6 +574,44 @@ func TestTask_loadSegmentsTask(t *testing.T) {
 		assert.NoError(t, err)
 	})
 
+	t.Run("test repeated load", func(t *testing.T) {
+		node, err := genSimpleQueryNode(ctx)
+		assert.NoError(t, err)
+
+		fieldBinlog, err := saveBinLog(ctx, defaultCollectionID, defaultPartitionID, defaultSegmentID, defaultMsgLength, schema)
+		assert.NoError(t, err)
+
+		req := &querypb.LoadSegmentsRequest{
+			Base:   genCommonMsgBase(commonpb.MsgType_LoadSegments),
+			Schema: schema,
+			Infos: []*querypb.SegmentLoadInfo{
+				{
+					SegmentID:    defaultSegmentID,
+					PartitionID:  defaultPartitionID,
+					CollectionID: defaultCollectionID,
+					BinlogPaths:  fieldBinlog,
+				},
+			},
+		}
+
+		task := loadSegmentsTask{
+			req:  req,
+			node: node,
+		}
+		// execute loadSegmentsTask twice
+		err = task.PreExecute(ctx)
+		assert.NoError(t, err)
+		err = task.Execute(ctx)
+		assert.NoError(t, err)
+		err = task.PreExecute(ctx)
+		assert.NoError(t, err)
+		err = task.Execute(ctx)
+		assert.NoError(t, err)
+		// expected only one segment in replica
+		num := node.historical.replica.getSegmentNum()
+		assert.Equal(t, 1, num)
+	})
+
 	t.Run("test execute grpc error", func(t *testing.T) {
 		node, err := genSimpleQueryNode(ctx)
 		assert.NoError(t, err)