*** a/doc/src/sgml/backup.sgml
--- b/doc/src/sgml/backup.sgml
***************
*** 859,864 **** SELECT pg_stop_backup();
--- 859,869 ----
      If you used the label to identify the associated dump file,
      then the archived history file is enough to tell you which dump file to
      restore.
+     Note that the WAL file name in the backup history file cannot be used
+     to determine which WAL files are required for the backup. Because it
+     indicates the subsequent WAL file of the starting or ending one for
+     the backup, when its location is exactly at a WAL file boundary (What
+     is worse, sometimes it indicates a nonexistent WAL file).
     </para>
  
     <para>