diff --git a/internal/querynodev2/pipeline/manager.go b/internal/querynodev2/pipeline/manager.go
index ba67753dd5c5da160638e4e676795ab2b83566a3..a4a3aa6ab18f99a44dac6a4e16825a77ec1fea28 100644
--- a/internal/querynodev2/pipeline/manager.go
+++ b/internal/querynodev2/pipeline/manager.go
@@ -49,10 +49,12 @@ type manager struct {
 
 	tSafeManager TSafeManager
 	dispatcher   msgdispatcher.Client
-	mu           sync.Mutex
+	mu           sync.RWMutex
 }
 
 func (m *manager) Num() int {
+	m.mu.RLock()
+	defer m.mu.RUnlock()
 	return len(m.channel2Pipeline)
 }
 
@@ -162,6 +164,5 @@ func NewManager(dataManager *DataManager,
 		delegators:       delegators,
 		tSafeManager:     tSafeManager,
 		dispatcher:       dispatcher,
-		mu:               sync.Mutex{},
 	}
 }