fix: L0 segment has been loaded to worker during channel balance (#37748

)

issue: #37703

---------

Signed-off-by: Wei Liu <wei.liu@zilliz.com>

internal/querynodev2/delegator/delegator_data.go

@@ -412,9 +412,16 @@ func (sd *shardDelegator) LoadSegments(ctx context.Context, req *querypb.LoadSeg
 	log := sd.getLogger(ctx)
 
 	targetNodeID := req.GetDstNodeID()
+	if len(req.GetInfos()) > 0 && req.GetInfos()[0].Level == datapb.SegmentLevel_L0 {
+		// force l0 segment to load on delegator
+		if targetNodeID != paramtable.GetNodeID() {
+			targetNodeID = paramtable.GetNodeID()
+			log.Info("unexpected L0 segment load on non-delegator node, force to load on delegator", zap.Int64("nodeIDInReq", req.GetDstNodeID()))
+		}
+	}
 	// add common log fields
 	log = log.With(
-		zap.Int64("workID", req.GetDstNodeID()),
+		zap.Int64("workID", targetNodeID),
 		zap.Int64s("segments", lo.Map(req.GetInfos(), func(info *querypb.SegmentLoadInfo, _ int) int64 { return info.GetSegmentID() })),
 	)
 
@@ -424,7 +431,7 @@ func (sd *shardDelegator) LoadSegments(ctx context.Context, req *querypb.LoadSeg
 		return err
 	}
 
-	req.Base.TargetID = req.GetDstNodeID()
+	req.Base.TargetID = targetNodeID
 	log.Debug("worker loads segments...")
 
 	sLoad := func(ctx context.Context, req *querypb.LoadSegmentsRequest) error {