Mailinglist Archive: opensuse-factory (381 mails)

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[opensuse-factory] A look on RPM compression in openSUSE

Compression performance plots are often done with something like the Silesia
corpus. Linux distributions have rather different proportions of file types, I
think. They have a lot of machine code, and even more data files, and probably
not so much text and images. Since our data set is also 2.8 orders of magnitude
bigger, rerunning a compression shootout will give more detail. So I did just
that.

http://paste.opensuse.org/15790105
http://inai.de/files/openSUSE-compression.ods
(My measurements included just *.x86_64.rpm + *.noarch.rpm.)

The takeaway from that is:

* xz outperforms zstd in the regions that xz caters to. But overall, xz
forms the far end of the "law of diminishing returns".

* Moving openSUSE from xz-5 to xz-2 saves 50% of time for an investment of
just 3.2 GB of space. Or, moving to zstd-7, saving 85% for ~6.1 GB.


Other observations:

* There are steps in compressor behavior, and that penalizes a lot of levels,
leaving only a few sensible ones: zstd-2-3-7-12, xz-1-2-3-4-5-9
(disregarding memory use, which is another factor).

* Some of our packages are too fat. kicad-packages takes longer to compress
than the entire remaining distro at zstd-19 with 16x-parallelism.
In other words, a sufficiently parallelized system
may have to wait just for that one to complete.

(* "Trend lines" in LibreOffice Calc are quite useless sometimes, as it does
not appear to calculate a constant offset portion for exp/pow fittings.)
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