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Re: Solving the compression dilema when rsync-ing Debian versions

>> So why not solve the compression problem at the root? Why not try to
>> change the compression in a way so it does produce a compressed
>> with the same (or similar) difference rate as the source? 
>Are you going to hack at *every* different kind of file format that you
>might ever want to rsync, to make it rsync friendly?
No, I want rsync not even to be mentioned. All I want is something
similar to

        gzip --compress-like=old-foo foo

where foo will be compressed as old-foo was or as aquivalent as
possible. Gzip does not need to know anything about foo except how it
was compressed. The switch "--compress-like" could be added to any
compression algorithmus (bzip?) as long as it's easy to retrieve the
compression scheme. Besides the following is completly legal but
probably not very sensible

        gzip --compress-like=foo bar

where bar will be compressed as foo even if they might be totally

Rsync-ing Debian packages will certainly take advantage of this solution
but the solution itself is 100% pure compression specific. Anything
which needs identical compression could profit from this switch. It's up
to profiting application to provide the necessary wrapper around.

>gzip --rsyncable, aloready implemented, ask Rusty Russell.

The --rsyncable switch might yield the same result (I haven't checked it
sofar) but will need some internal knowledge how to determine the old

As I read my mail again the syntax for "compressing like" could be

        gzip --compress=foo bar

where bar is compressed as foo was. Foo is of course a compressed file
(how else could the compression be retrieved) while bar is not.

O. Wyss

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