diff --git a/docs/developer_guides/chap09_data_coord.md b/docs/developer_guides/chap09_data_coord.md
index 1e929fbacf..85060376e3 100644
--- a/docs/developer_guides/chap09_data_coord.md
+++ b/docs/developer_guides/chap09_data_coord.md
@@ -19,6 +19,7 @@ type DataCoord interface {
 	GetSegmentStates(ctx context.Context, req *datapb.GetSegmentStatesRequest) (*datapb.GetSegmentStatesResponse, error)
 	// GetInsertBinlogPaths requests binlog paths for specified segment
 	GetInsertBinlogPaths(ctx context.Context, req *datapb.GetInsertBinlogPathsRequest) (*datapb.GetInsertBinlogPathsResponse, error)
+  // GetSegmentInfoChannel legacy API, returns segment info statistics channel
 	GetSegmentInfoChannel(ctx context.Context) (*milvuspb.StringResponse, error)
   // GetCollectionStatistics requests collection statistics
 	GetCollectionStatistics(ctx context.Context, req *datapb.GetCollectionStatisticsRequest) (*datapb.GetCollectionStatisticsResponse, error)