diff --git a/ast/misc.go b/ast/misc.go
index 8e1929824..f3b55edf3 100644
--- a/ast/misc.go
+++ b/ast/misc.go
@@ -754,14 +754,14 @@ type KillStmt struct {
 	// If Query is false, terminates the connection associated with the given ConnectionID, after terminating any statement the connection is executing.
 	Query        bool
 	ConnectionID uint64
-	// TiDBExtension is used to indicate whether the user knows he is sending kill statement to the right tidb-server.
+	// TiDBExtension is deprecated, and has no effect. See TiDB issue #8854.
+	// It had been used to indicate whether the user knows he is sending kill statement to the right tidb-server.
 	// When the SQL grammar is "KILL TIDB [CONNECTION | QUERY] connectionID", TiDBExtension will be set.
 	// It's a special grammar extension in TiDB. This extension exists because, when the connection is:
 	// client -> LVS proxy -> TiDB, and type Ctrl+C in client, the following action will be executed:
 	// new a connection; kill xxx;
 	// kill command may send to the wrong TiDB, because the exists of LVS proxy, and kill the wrong session.
 	// So, "KILL TIDB" grammar is introduced, and it REQUIRES DIRECT client -> TiDB TOPOLOGY.
-	// TODO: The standard KILL grammar will be supported once we have global connectionID.
 	TiDBExtension bool
 }