Re: Rsyncable GZIP (was Re: Package metadata server)
On 7 Apr 2002, Robert Tiberius Johnson wrote:
> On Sun, 2002-04-07 at 11:16, Otto Wyss wrote:
> > What amazes me is that nobody is able or willing to provide any figures.
> > So I guess no provider of an rsync server is interested in this subject
> > and therefore it can't be a big problem.
>
> Here are some experiments, and a mathematical analysis of different
> approaches. The only missing piece of data that I had to fudge is: how
> often do people run apt-get update? If anyone can give me server logs
> containing If-Modified-Since fields, that would be great.
>
> Quick Summary:
> ------------------
> Diffs compressed with bzip2 generated the smallest difference files, and
> hence the smallest downloads. Using the scheme described below, I
> estimate that mirrors retaining 20 days worth of diffs will need about
> 159K of disk space per Packages file and the average 'apt-get update'
> will transfer about 24.2K per changed Packages file.
54 days with of Packages(sid/main/i386) gives 900k of xdeltas.
> xdelta would have slightly higher bandwidth and disk space requirements,
> but would be applicable to binary files (such as debs). rsync has no
> disk space requirements, but uses 10 times as much bandwidth and
> requires more memory, cpu power, etc, on the server. rsync also has the
> advantage of already being implemented, but managing a series of diffs
> seems like a trivial shell script.
xdelta would not work with debs. It doesn't understand archives.
xdelta does understand already compressed files, and will actually decompres
the files first, before generating the diff.
The problem with xdelta tho, is that it requires both old and new version to
be available on the same side of the link, to do it's magic.
Is someone interested in modifying xdelta to read archives(ar, tar, cpio)?
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