Log Message:
-----------
Improve the documentation on 8.4 visibility map related VACUUM changes.
Explain how vacuum_freeze_table_age should be tuned, and how it relates
to the other settings. Mention that vacuum_freeze_table_age also affects
when autovacuum scans the whole table.
Modified Files:
--------------
pgsql/doc/src/sgml:
maintenance.sgml (r1.92 -> r1.93)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/maintenance.sgml?r1=1.92&r2=1.93)