[Debian-med-packaging] Question about proper archive area for packages that require big data for operation

[Ben Hutchings]

On Fri, Apr 26, 2013 at 03:21:43PM +0200, Laszlo Kajan wrote:
> Dear FTP Masters!
> 
> On 23/04/13 15:13, Benjamin Drung wrote:
> [...]
> > You can use xz for the source and binary package to reduce the size. The
> > default compression level for xz reduces the size of the source tarball
> > from 415 MB to 272 MB:
> > 
> > $ ls -1s --si metastudent-data_1.0.0.tar*
> > 823M metastudent-data_1.0.0.tar
> > 381M metastudent-data_1.0.0.tar.bz2
> > 415M metastudent-data_1.0.0.tar.gz
> > 272M metastudent-data_1.0.0.tar.xz
> > $ ls -1sh metastudent-data_1.0.0.tar*
> > 784M metastudent-data_1.0.0.tar
> > 363M metastudent-data_1.0.0.tar.bz2
> > 396M metastudent-data_1.0.0.tar.gz
> > 259M metastudent-data_1.0.0.tar.xz
> 
> Following Benjamin's suggestion and the data.debian.org document [1], we have prepared a 'metastudent-data' arch:all package that is ~130MB (xz
> compressed).
> The package builds required architecture dependent databases in the postinst script. The purpose of this is to save space in the archive that
> each architecture dependent version would take up.
[...]

Does this mean that installing the package results in having two
uncompressed copies of the data on disk?  If so, wouldn't it be
better to do:

1. Compress the database (with xz).
2. Build the package without compression (contents are already
   compressed so re-compressing would be a waste of time).
3. In postinst, decompress and convert the database to native.

However, I would expect the vast majority of installations to be on
amd64, so if you always generate a 64-bit little-endian database
and avoid duplicating when installing on such a machine then it
would be better for most users (not so nice for others).

(Incidentally, arch:all packages generating arch-specific data have
interesting interactions with multi-arch.  I doubt many people with
multi-arch systems would want this package to generate multiple
versions of the database, but you never know...)

Ben.

-- 
Ben Hutchings
We get into the habit of living before acquiring the habit of thinking.
                                                              - Albert Camus