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Re: Limiting the size of installed changelogs

On Thu, Sep 13, 2018 at 11:22:37AM +0100, Ben Hutchings wrote:
> The src:linux package has a very big changelog (about 1700 kiB
> uncompressed, 600 kiB gzipped).  On my system the largest installed
> changelogs, by some way, are all versions of this.  (The next largest
> changelogs come from src:glibc, at about 200 kiB gzipped.)

I was curious, so I ran the following on my laptop:

$ find /usr/share/doc -name '*changelog*' -printf '%s %p\n' | sort -n | tail -n10 | while read size path; do echo $(humanify "$size") "$path"; done
2 MB /usr/share/doc/libgstreamer-plugins-bad1.0-0/changelog.gz
2 MB /usr/share/doc/xserver-common/changelog.gz
2 MB /usr/share/doc/xserver-xephyr/changelog.gz
2 MB /usr/share/doc/xserver-xorg-core/changelog.gz
2 MB /usr/share/doc/xserver-xorg-legacy/changelog.gz
2 MB /usr/share/doc/xwayland/changelog.gz
2 MB /usr/share/doc/gimp/changelog.gz
2 MB /usr/share/doc/gimp-data/changelog.gz
2 MB /usr/share/doc/libgimp2.0/changelog.gz
4 MB /usr/share/doc/libvirt0/changelog.gz

While changelogs are sometimes really useful, that's a fair bit of
diskspace on my laptop, and a fair bit of bandwidth to transfer, for
fairly little gain.

> The older history is unlikely to be of any use to users.  So on smaller
> systems this could be a significant waste of space.  (I know it's
> possible to filter out the installation of docs entirely, but I don't
> think this option is well known.)

I agree that we can drop older changelog entries. I suggest truncating
changelogs, at least large ones, by dropping any entries from before
stable, when uploading to unstable. So uploading to unstable today,
any entries from before stretch can be dropped. When a changelog is
truncated, there should be a URL to the full changelog, so those who
really are curious can find it. (Possibly oldstable would be a better
cut-off point.)

Alternatively, we could change things so that the changelog for each
Debian release (major part of version) is put in its own file.

With this scheme, uploads to unstable today would have
/usr/share/doc/*/changelog.debian10.gz. Once buster is released,
uploads would include changelog.debian11.gz instead. This would allow
a fairly natural rotation.

> - Does it make sense to compress changelogs with xz?  For src:linux,
> this achieves about a 20-25% reduction over gzip.

I'd be OK with using xz -9 to compress changelogs. This would also be
easily doable in debhelper. From the ten files I showed at the
beginning, I get about a 29% savings recompressing as xz.

I want to build worthwhile things that might last. --joeyh

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