Additional docs for toast_tuple_target changes

doc/src/sgml/storage.sgml

@@ -429,7 +429,7 @@ when a row value to be stored in a table is wider than
 <symbol>TOAST_TUPLE_THRESHOLD</symbol> bytes (normally 2 kB).
 The <acronym>TOAST</acronym> code will compress and/or move
 field values out-of-line until the row value is shorter than
-<symbol>TOAST_TUPLE_TARGET</symbol> bytes (also normally 2 kB)
+<symbol>TOAST_TUPLE_TARGET</symbol> bytes (also normally 2 kB, adjustable)
 or no more gains can be had.  During an UPDATE
 operation, values of unchanged fields are normally preserved as-is; so an
 UPDATE of a row with out-of-line values incurs no <acronym>TOAST</acronym> costs if
@@ -483,6 +483,11 @@ of that data type, but the strategy for a given table column can be altered
 with <link linkend="sql-altertable"><command>ALTER TABLE ... SET STORAGE</command></link>.
 </para>
 
+<para>
+<symbol>TOAST_TUPLE_TARGET</symbol> can be adjusted for each table using
+<link linkend="sql-altertable"><command>ALTER TABLE ... SET (toast_tuple_target = N)</command></link>
+</para>
+
 <para>
 This scheme has a number of advantages compared to a more straightforward
 approach such as allowing row values to span pages.  Assuming that queries are