Presto: A project to add delta rpm support into yum for Fedora users
http://hosted.fedoraproject.org/projects/presto.  A list of presto-enabled
repositories is available there.

Installation:
=============
1. Install yum-presto on your system (yum -y install yum-presto)
2. If your Fedora repositories aren't presto-enabled, find a mirror that is and
   set your baseurl to point to it.  See the web site for a list of
   presto-enabled Fedora mirrors.
3. Now install an old rpm from a presto-enabled repository using rpm, then
   try updating it using yum. The plugin should kick in, try to download the
   drpm, reconstruct the full rpm, and yum should install that.

Configuration file:
======
/etc/yum/pluginconf.d/presto.conf has the following options in [main]:
keepdeltas=1                Always keep deltas in cache no matter what keepcache
                            is set to.
neverkeepdeltas=1 (default) Always remove deltas after creating full rpms.

Note: If you specify neither keepdeltas nor neverkeepdeltas, presto will follow
      the keepcache option in yum.conf.