Add note that autovacuum can use up several times maintenance_work_mem,

with warning against setting it too high.

doc/src/sgml/config.sgml

-<!-- $PostgreSQL: pgsql/doc/src/sgml/config.sgml,v 1.198 2008/11/21 20:21:59 tgl Exp $ -->
+<!-- $PostgreSQL: pgsql/doc/src/sgml/config.sgml,v 1.199 2008/12/08 15:11:39 mha Exp $ -->
 
 <chapter Id="runtime-config">
   <title>Server Configuration</title>
@@ -881,6 +881,11 @@ SET ENABLE_SEQSCAN TO OFF;
         than <varname>work_mem</varname>.  Larger settings might improve
         performance for vacuuming and for restoring database dumps.
        </para>
+       <para>
+        Note that when autovacuum runs, up to
+        <xref linkend="guc-autovacuum-max-workers"> times this memory may be
+        allocated, so be careful not to set the default value too high.
+       </para>
       </listitem>
      </varlistentry>