Add URLs for :

* Speed WAL recovery by allowing more than one page to be prefetched

  This involves having a separate process that can be told which pages
  the recovery process will need in the near future.

>   http://archives.postgresql.org/pgsql-general/2007-12/msg00683.php
>   http://archives.postgresql.org/pgsql-hackers/2007-12/msg00497.php
<