diff --git a/src/backend/cdb/cdbdatalocality.c b/src/backend/cdb/cdbdatalocality.c
index 6e95130..d2cfd72 100644
--- a/src/backend/cdb/cdbdatalocality.c
+++ b/src/backend/cdb/cdbdatalocality.c
@@ -260,9 +260,9 @@
  * structure for target segment ID mapping.
  */
 typedef struct TargetSegmentIDMap {
-	int target_segment_num;
-	int *global_IDs;
-	char** hostname;
+	int target_segment_num;   // number of virtual segments
+	int *global_IDs;   // virtual segment number -> global hostIndex
+	char** hostname;   // hostname of each virtual segment
 } TargetSegmentIDMap;
 
 /*