Subject: debdelta: Avoid generating the actual `.deb`
Package: debdelta
Version: 0.67
Severity: wishlist

Dear Maintainer,

`debdelta-upgrade` is great at reducing the amount of data downloaded,
but on some of my (weaker) machines, generating the `.deb` files takes
a lot of time, and for no good reason: 99% of the time is spent not
applying the xdelta but (re)compressing the result with `xz`.

So, this wishlist item is to change APT such that we can skip the
generation of the `.deb` file and instead keep the old `.deb` together
with the patch(es) in `/var/cache/apt/archives`.
When APT needs to install the (not created) `.deb`, instead of
unpacking+uncompressing the (not created) `.deb`, it would
unpack+uncompress the old `.deb`, and apply the (set of) patch(es).

Since the old `.deb` + patch(es) is usually larger than
a patched+recompressed `.deb`, we could occasionally "repack" the files
in `/var/cache/apt/archives`, but that would be optional and could be
performed opportunistically in the background, a bit like Git's GC.


        Stefan


-- System Information:
Debian Release: trixie/sid
  APT prefers testing
  APT policy: (990, 'testing'), (500, 'stable-security'), (100, 'stable')
Architecture: i386 (x86_64)
Foreign Architectures: amd64

Kernel: Linux 6.1.0-7-amd64 (SMP w/2 CPU threads; PREEMPT)
Kernel taint flags: TAINT_WARN, TAINT_OOT_MODULE, TAINT_UNSIGNED_MODULE
Locale: LANG=fr_CH.UTF-8, LC_CTYPE=fr_CH.UTF-8 (charmap=UTF-8), LANGUAGE not se$
Shell: /bin/sh linked to /usr/bin/dash
Init: systemd (via /run/systemd/system)
LSM: AppArmor: enabled

Versions of packages debdelta depends on:
ii  binutils          2.41-6
ii  bzip2             1.0.8-5+b1
ii  libbz2-1.0        1.0.8-5+b1
ii  libc6             2.37-12
ii  python3           3.11.4-5+b1
ii  python3-requests  2.31.0+dfsg-1
ii  zlib1g            1:1.2.13.dfsg-3

Versions of packages debdelta recommends:
ii  bsdiff                   4.3-23
ii  gnupg2                   2.2.40-1.1
ii  gpg-agent [gnupg-agent]  2.2.40-1.1
ii  lzma                     9.22-2.2
ii  python3-apt              2.6.0
ii  python3-debian           0.1.49
ii  xdelta                   1.1.3-10.4
ii  xdelta3                  3.0.11-dfsg-1.2
ii  xz-utils [lzma]          5.4.4-0.1

Versions of packages debdelta suggests:
pn  debdelta-doc  <none>

-- no debconf information

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