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Re: .deb format: let's use 0.939, zstd, drop bzip2




On Wed, May 08, 2019 at 10:35:58PM +0200, Ansgar wrote:
> Adam Borowski writes:
> > I've recently did some research on how can we improve the speed of unpacking
> > packages.  There's a lot of other stages that can be improved, but let's
> > talk about the .deb format.
> >
> > First, the 0.939 format, as described in "man deb-old".  While still being
> > accepted by dpkg, it had been superseded before even the very first stable
> > release.  Why?  It has at least two upsides over 2.0:
> 
> Switching to a different binary format will break various tools.

The 0.939 format is already supported by most tools.

No one sane digs into insides of the format, using a small number of
low-level tools, thus we can reuse it with little effort.

Of course, adding a new compressor _does_ break compat, but we added four
compressors to 2.0 over the years already, and the sky didn't fall.

> If we want to do this, I wonder if we shouldn't take the chance to move
> away from tar?

Any seekable format significantly reduces compression, although this can
be reduced by managing split points.

> We have various applications that only want to extract single members of
> the package (changelog, NEWS, copyright, ...); tar is a really bad
> format for such an operation.  Other formats (zip, 7z, ...) are more
> suited for them.

Perhaps such files could be considered metadata and moved to the control
tarball?  Or merely just moved forward -- remember that tarballs are
unordered.


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