Bug#832010: Please enable LZ4 compression

[Zbigniew Jędrzejewski-Szmek]

On Thu, Jul 21, 2016 at 07:28:26PM +0200, Yuri D'Elia wrote:
> On Thu, Jul 21 2016, Michael Biebl <biebl at debian.org> wrote:
> > And in Debian we build against libxz, so xz compression is used for core
> > files.
> 
> Indeed, and it's pretty slow.
> 
> > What would we gain by switching from xz to lz4. Can you provide numbers?
> 
> I don't have enough time to back it up comparing exactly the difference
> between LZ4 and XZ in coredump, but if you compare regular XZ to LZ4 you
> can expect anywhere between 10x and 50x improvement in compression
> speed while maintaining an acceptable compression ratio.

systemd itself includes a benchmark:

$ ./test-compress-benchmark
XZ/zeros: compressed & decompressed 57898278 bytes in 2.02s (27.37MiB/s), mean compresion 99.96%, skipped 0 bytes
LZ4/zeros: compressed & decompressed 2031958921 bytes in 2.00s (968.65MiB/s), mean compresion 99.60%, skipped 0 bytes
XZ/simple: compressed & decompressed 58918934 bytes in 2.01s (27.97MiB/s), mean compresion 99.95%, skipped 0 bytes
LZ4/simple: compressed & decompressed 2544957269 bytes in 2.00s (1213.26MiB/s), mean compresion 99.60%, skipped 0 bytes
XZ/random: compressed & decompressed 12258687 bytes in 2.08s (5.62MiB/s), mean compresion 44.33%, skipped 168354 bytes
LZ4/random: compressed & decompressed 2235751628 bytes in 2.00s (1065.61MiB/s), mean compresion 44.94%, skipped 24251355 bytes

You can also specify different test time as an argument.

Zbyszek