Bug#1066828: xz-utils: worse compression ratio should be announced in NEWS.Debian

[Vincent Lefevre]

On 2024-03-14 00:35:53 +0100, Vincent Lefevre wrote:
> Since this affects what the user gets and is some kind of regression,
> this should be announced in NEWS.Debian, IMHO.

As an example of how this can affect the user, this introduced a
serious bug in pristine-tar:
  https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1063252
(what is expected here can also be expected by the end user for
his own needs...)

-- 
Vincent Lefèvre  - Web: 
100% accessible validated (X)HTML - Blog: 
Work: CR INRIA - computer arithmetic / AriC project (LIP, ENS-Lyon)

Bug#1066828: xz-utils: worse compression ratio should be announced in NEWS.Debian

[Vincent Lefevre]

Package: xz-utils
Version: 5.6.0-0.2
Severity: wishlist

After upgrading xz-utils from 5.4.5-0.3 to 5.6.0-0.2, the compression
ratio with "xz -9" has decreased. For instance, on 3 files:

Old   118822308   146463040   157197172
New   121120576   148930624   161255000

It took me some time to figure out. This is the reason:

/usr/share/doc/xz-utils/NEWS.gz

5.6.0 (2024-02-24)

[...]
* xz:

- Multithreaded mode is now the default. This improves
  compression speed and creates .xz files that can be
  decompressed in multithreaded mode. The downsides are
  increased memory usage and slightly worse compression ratio.
[...]

Using -T1 restores the old behavior.

Since this affects what the user gets and is some kind of regression,
this should be announced in NEWS.Debian, IMHO.

Note also that this change might affect diffs between .xz files (e.g.
after something is appended to the uncompressed file), though I have
not checked.

-- System Information:
Debian Release: trixie/sid
  APT prefers unstable-debug
  APT policy: (500, 'unstable-debug'), (500, 'stable-updates'), (500, 
'stable-security'), (500, 'stable-debug'), (500, 'proposed-updates-debug'), 
(500, 'unstable'), (500, 'testing'), (500, 'stable'), (1, 'experimental')
Architecture: amd64 (x86_64)

Kernel: Linux 6.6.15-amd64 (SMP w/16 CPU threads; PREEMPT)
Locale: LANG=C.UTF-8, LC_CTYPE=C.UTF-8 (charmap=UTF-8), LANGUAGE not set
Shell: /bin/sh linked to /usr/bin/dash
Init: systemd (via /run/systemd/system)
LSM: AppArmor: enabled

Versions of packages xz-utils depends on:
ii  libc6 2.37-15.1
ii  liblzma5  5.6.0-0.2

xz-utils recommends no packages.

xz-utils suggests no packages.

-- no debconf information

-- 
Vincent Lefèvre  - Web: 
100% accessible validated (X)HTML - Blog: 
Work: CR INRIA - computer arithmetic / AriC project (LIP, ENS-Lyon)