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Re: Autoexpanding ZIP archives?

From: Ben Collins-Sussman <sussman_at_red-bean.com>
Date: 2005-12-07 18:47:38 CET

On 12/7/05, Hadmut Danisch <hadmut@danisch.de> wrote:
> On Wed, Dec 07, 2005 at 10:17:22AM -0600, Ben Collins-Sussman wrote:
> >
> > Try it yourself: make a .zip presentation with 10MB of graphics and
> > commit it to an svn repository. Change one word in the presentation.
> > Now commit that new .zip to the repository. The repository's size
> > should only grow by the binary difference between the 2 zip files. I
> > don't believe that every single byte will be different, maybe 50% of
> > them will. So I would expect the repository to grow to 15MB, not
> > 20MB.
>
>
> The zip archives store everything with a modification date. So just
> slight changes can cause large differenes. Keep in mind that LZ
> compression is not byte aligned. A change of just a single bit in the
> uncompressed source (e.g. the mod date of a directory) could leave the
> 10 MB unmodified in principle, but shift it by one bit. The full
> archive is modified, 10 MB of storage wasted.

Yes, you've successfully described a possible pathological worst-case
scenario. Nobody disagrees. What ghudson and I are saying is that on
*average*, it will probably only be a 5MB delta, not a 10MB one.

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Received on Wed Dec 7 18:49:09 2005

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