fix: add new comment

Signed-off-by: hlts2 <hiroto.funakoshi.hiroto@gmail.com>

pkg/gateway/mirror/handler/grpc/handler.go

@@ -976,6 +976,9 @@ func (s *server) Insert(ctx context.Context, req *payload.Insert_Request) (loc *
 		return loc, nil
 	}
 
+	// If this condition is matched, it means the request from user.
+	// So this component sends requests to other Mirror gateways and the Vald gateway (LB gateway) of its own cluster.
+
 	var mu sync.Mutex
 	var result sync.Map[string, *errorState] // map[target host: error state]
 	loc = &payload.Object_Location{
@@ -1471,6 +1474,9 @@ func (s *server) Update(ctx context.Context, req *payload.Update_Request) (loc *
 		return loc, nil
 	}
 
+	// If this condition is matched, it means the request from user.
+	// So this component sends requests to other Mirror gateways and the Vald gateway (LB gateway) of its own cluster.
+
 	var mu sync.Mutex
 	var result sync.Map[string, *errorState] // map[target host: error state]
 	loc = &payload.Object_Location{
@@ -1997,6 +2003,9 @@ func (s *server) Upsert(ctx context.Context, req *payload.Upsert_Request) (loc *
 		return loc, nil
 	}
 
+	// If this condition is matched, it means the request from user.
+	// So this component sends requests to other Mirror gateways and the Vald gateway (LB gateway) of its own cluster.
+
 	var mu sync.Mutex
 	var result sync.Map[string, *errorState] // map[target host: error state]
 	loc = &payload.Object_Location{
@@ -2354,6 +2363,9 @@ func (s *server) Remove(ctx context.Context, req *payload.Remove_Request) (loc *
 		return loc, nil
 	}
 
+	// If this condition is matched, it means the request from user.
+	// So this component sends requests to other Mirror gateways and the Vald gateway (LB gateway) of its own cluster.
+
 	var mu sync.Mutex
 	var result sync.Map[string, *errorState] // map[target host: error state]
 	loc = &payload.Object_Location{
@@ -2707,6 +2719,9 @@ func (s *server) RemoveByTimestamp(ctx context.Context, req *payload.Remove_Time
 		return locs, nil
 	}
 
+	// If this condition is matched, it means the request from user.
+	// So this component sends requests to other Mirror gateways and the Vald gateway (LB gateway) of its own cluster.
+
 	var mu sync.Mutex
 	var result sync.Map[string, *errorState] // map[target host: error state]
 	locs = new(payload.Object_Locations)