Fedora 12 and Yum Presto Plugin
Though yum-presto plugin that enables the end users to consume delta RPMs or binary diffs of updates has been in Fedora for a long time, Fedora 11 was the first Fedora release to provide it in a more integrated capacity. Bodhi, the Fedora updates system will push out delta RPM’s along with the full RPM’s and createrepo can generate delta RPMs for your custom repositories as well.
All you had to do to enable it was just yum install yum-presto and boom, you had much faster updates and less bandwidth usage. There is a trade off however in slightly higher CPU consumption while installing those updates since the full RPMs are actually generated on the disk before installing them however most users do enjoy the benefits.
In Fedora 12, I had expected yum-presto to be made available by default and that didn’t happen due to various people and process issues. However many users will still get it by default. Here is why:
I added it to the GNOME Desktop group after talking to the Desktop team and KDE SIG has added it to the KDE Live CD kickstart file instead (for users using the dvd or installing KDE post-installation, you have to install yum-presto plugin seprately). So the benefits are available to more people out of the box in Fedora 12.
Jonathan Dieter (maintainer of yum-presto plugin) did come up with a couple of problems that he suggested needs to be fixed before release. The second bug which causes more CPU usage has been fixed by setting LZMA compression level to 2 in redhat-rpm-config package. It appears that LZMA compression format has a problem which is exposed by deltarpm that results in the first bug. Apparently it requires changes in the build system or the software to be patched to workaround it. Otherwise uses will see a MD5 mismatch error when yum-presto downloads the drpm for some noarch (architecture independent packages such as documentation, fonts and scripts) and it will fall back to downloading the full RPM instead. Even with this problem, yum-presto is still very useful. Not sure whether we are making the changes to the build system or fixing the format before Fedora 12 release. If anyone is taking care of that, let me know.