diff --git a/docs/developer_guides/chap08_binlog.md b/docs/developer_guides/chap08_binlog.md
index 654739a604737..04ca8ce593bd1 100644
--- a/docs/developer_guides/chap08_binlog.md
+++ b/docs/developer_guides/chap08_binlog.md
@@ -54,11 +54,11 @@ Binlog file consists of 4 bytes magic number and a series of events. The first e
 |        +----------------------------+---------------------------------------------------------------------+
 |        | PayloadDataType  65 : 4    | data type of payload                                                |
 |        +----------------------------+---------------------------------------------------------------------+
+|        | PostHeaderLengths n : n    | header lengths for all event types                                  |
+|        +----------------------------+---------------------------------------------------------------------+
 |        | ExtraLength      69 : 4    | length of extra information                                         |
 |        +----------------------------+---------------------------------------------------------------------+
 |        | ExtraBytes       73 : n    | extra information in json format                                    |
-|        +----------------------------+---------------------------------------------------------------------+
-|        | PostHeaderLengths n : n    | header lengths for all event types                                  |
 +=====================================+=====================================================================|
 ```
 
diff --git a/internal/storage/data_codec.go b/internal/storage/data_codec.go
index 0794c17a2ccba..237582a3a5792 100644
--- a/internal/storage/data_codec.go
+++ b/internal/storage/data_codec.go
@@ -286,6 +286,7 @@ func (insertCodec *InsertCodec) Serialize(partitionID UniqueID, segmentID Unique
 	startTs := ts[0]
 	endTs := ts[len(ts)-1]
 
+	// sort insert data by rowID
 	dataSorter := &DataSorter{
 		InsertCodec: insertCodec,
 		InsertData:  data,