[systemd-devel] [systemd-commits] 14 commits - configure.ac Makefile.am Makefile-man.am man/coredump.conf.xml src/core src/journal src/shared

[Zbigniew Jędrzejewski-Szmek]

On Fri, Jun 27, 2014 at 03:22:50PM +0200, Lennart Poettering wrote:
> On Wed, 25.06.14 22:49, Zbigniew Jędrzejewski-Szmek (zbyszek at kemper.freedesktop.org) wrote:
> 
> > +      <varlistentry>
> > +        <term><varname>Compression=</varname></term>
> > +
> > +        <listitem><para>Controls the type of compression for external
> > +        storage. One of <literal>xz</literal> or
> > +        <literal>none</literal>.</para>
> > +        </listitem>
> > +      </varlistentry>
> > +
> > +      <varlistentry>
> > +        <term><varname>CompressionLevel=</varname></term>
> > +
> > +        <listitem><para>Controls the level of compression for external
> > +        storage. An integer between 0 and 9. See
> > +        <citerefentry><refentrytitle>xz</refentrytitle><manvolnum>1</manvolnum></citerefentry>
> > +        for more details.</para></listitem>
> > +      </varlistentry>
> 
> Hmm. Do we really want CompressionLevel= as an integer here? It sounds
> awfully low-level and implementation-detailish to me. I#d rather keep
> this as close and simple as the compression settings in journald.conf:
> i.e. a single boolean Compress=, and that's it. The fact that XZ is
> mostly an implementation detail I think, and compression levels should
> just be chosen right.
Hm, I did some testing, and I'm not convinced that XZ is the right
compressor for the job.

First I generated a 1GB coredump of Python with random patterns. It
takes 20 minutes (!)  to compress with XZ 9, and 11.5 min with XZ 6,
~1 min with gzip 6, the same with gzip 9. The gain from XZ compression
is an increase in compression: gzip saves 7%, XZ saves 12%.

Second I generated a second 1GB coredump, highly compressible.
XZ 9 → 99.8%, 120 s; XZ 6 → 99.8%, 120 s;
gzip 6 → 99.6%, 11 s; gzip 9 → 99.6%, 13 s;

So the tradeoffs seem all wrong.

> Zbigniew, would you be terribly disappointed if I simplify this and
> bring this more in line with journald.conf?
Yeah, go ahead.

Zbyszek