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When I do a yum install or a yum update, sometimes I get this

Loaded plugins: presto, refresh-packagekit

telling me that the packages are being updated.

What is presto?

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Only in a geek community could you ask a question like this without people questioning your sanity. ;-) I have no idea what you are asking, but my first instinct was to open up the question so I could find out what yum and presto are. Sure enough there are several excellent answers with links to explain both. – Wayne Johnston Aug 2 '10 at 0:25
up vote 8 down vote accepted

Presto makes yum download only the delta. The changes. It downloads them and apply them on the existing data, thus it saves a lot of bandwidth. (You pay with Disk IO and CPU load instead.)

It is a really good thing for developing countries, people with mobile internet and so on.

ps.: OpenSUSE been using this for a long time. If I remember clearly they were the first RPM based delta users, but fixme, I'm not sure about this. (openSUSE downloads delta, apply, install package. On Fedora: Download all delta, apply them, install them all.)

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beaten by 20 seconds >.< – Sathya Aug 1 '10 at 19:33
Sorry man... :D – Shiki Aug 1 '10 at 19:33
The extra disk IO and CPU load is negligible compared to the bandwidth saving. – Zaz Aug 2 '10 at 9:19
Indeed. I just wanted to say you pay with those. Like some admin said: "Currently, bandwidth is cheaper". That's why some smaller distro won't ship this since they dont have enough resource on the servers. – Shiki Aug 2 '10 at 10:27

It adds support for delta-RPMs which use a delta-transfer algorithm to save time downloading. Basically, presto won't download the entire package, only the changes since the last version.

Fedora Wiki:

The presto plugin for yum adds support for downloading deltarpms and using them to generate new packages. If user enables this plugin, it will make a substantial dent in the amount of data having to be downloaded for updates.

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Delta-RPM, not deb. Fedora uses RPM. – Sathya Aug 1 '10 at 19:44
@Sathya: Whoops, fixed now. – Zaz Aug 1 '10 at 22:49

Presto is a plugin which enables Delta RPM support in yum. Basically, deltaRPM creates a new RPM based on the diffs of the new and previous version - saving on bandwidth and time required to download, since only the "changed" bits will be downloaded, instead of the full monolithic package.

More details:

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