Re: Proposal: A new approach to differential debs

[Jonathan Nieder <jrnieder@gmail.com>]

Hi,

Julian Andres Klode wrote:

> Today's research has shown that rolling hashes do not perform well
> on executables because of changing offsets and so on destroying the
> hashes. There were no measurable space savings when adding fairly
> similar firefox releases to either a casync or borg repository -
> and that's on uncompressed tarballs of the latest 2 firefox uploads.

For the same reason, compressors like xz apply a filter to executables
before using more generic compression algorithms on them.  See e.g.
https://git.tukaani.org/?p=xz.git;a=blob;f=src/liblzma/simple/x86.c
(and the rest of the filters in that directory).

Thanks and hope that helps,
Jonathan