Clarify vacuum lazy can shrink a file under certain circumstances.

diff --git a/doc/src/sgml/maintenance.sgml b/doc/src/sgml/maintenance.sgml
index 66356c0d012540e04abf057678d3a0cf41d3ffba..a3800c60822a7a6d5377c1df9b32c344f0da8466 100644 (file)
--- a/doc/src/sgml/maintenance.sgml
+++ b/doc/src/sgml/maintenance.sgml
@@ -1,5 +1,5 @@
 
 
 
@@ -141,11 +141,12 @@ $PostgreSQL: pgsql/doc/src/sgml/maintenance.sgml,v 1.51 2005/11/04 23:14:00 pete
     command. The first form, known as lazy vacuum or
     just VACUUM, marks expired data in tables and
     indexes for future reuse; it does not attempt
-    to reclaim the space used by this expired data
-    immediately. Therefore, the table file is not shortened, and any
-    unused space in the file is not returned to the operating
-    system. This variant of VACUUM can be run
-    concurrently with normal database operations.
+    to reclaim the space used by this expired data unless the space is
+    at the end of the table and an exclusive lock can be obtained easily
+    on the table. Unused space at the start or middle of the file does
+    not result in the file being shortened and space returned to the
+    operating system. This variant of VACUUM can be
+    run concurrently with normal database operations.