Comments for wsrep_exec_mode's.

sql/wsrep_mysqld.h

@@ -28,9 +28,16 @@ class set_var;
 class THD;
 
 enum wsrep_exec_mode {
+  /* Transaction processing before replication. */
   LOCAL_STATE,
+  /* Slave thread applying write sets from other nodes or replaying thread. */
   REPL_RECV,
+  /* Total-order-isolation mode */
   TOTAL_ORDER,
+  /*
+    Transaction procession after it has been replicated in prepare stage and
+    has passed certification
+  */
   LOCAL_COMMIT
 };