Mention that tables have a visibility map fork alongside the main fork

and FSM.

diff --git a/doc/src/sgml/storage.sgml b/doc/src/sgml/storage.sgml
index 777f81a066a5e90d61bdf84a16346f51db2da0a6..daf47411e6706f78e865a5e751061bc92dee02ae 100644 (file)
--- a/doc/src/sgml/storage.sgml
+++ b/doc/src/sgml/storage.sgml
@@ -134,7 +134,9 @@ or index's <firstterm>filenode</> number, which can be found in
 main file (aka. main fork), a <firstterm>free space map</> (see
 <xref linkend="storage-fsm">) that stores information about free space
 available in the relation, is stored in a file named after the filenode
-number, with the the <literal>_fsm</> suffix.
+number, with the <literal>_fsm</> suffix.  Tables also have a visibility map
+fork, with the <literal>_vm</> suffix, to track which pages are known to have
+no dead tuples and therefore need no vacuuming.
 </para>
 
 <caution>