On Sat, Jul 21, 2012 at 11:42:03AM -0400, Joey Hess wrote: > Hideki Yamane wrote: > > On Sun, 8 Jul 2012 17:58:16 +0200 > > Adam Borowski <kilob...@angband.pl> wrote: > > > • xz -6 (the default) is a lot slower when compressing, fast when > > > decompressing, needs only 10MB memory, 58% size > > > • xz -9 has very slow compression, takes gobs of memory, 56% size > > > (Obviously, the "size" numbers are dragged down by uncompressible > > > files > > > when you look at the whole archive.) > > > > I tested as well, and sometimes decompression with xz is so sloooow, > > it takes 6-8 times than default gz. > > I was just watching your DebConf presentation "Lets shrink Debian > package archive" and I think there you said decompression with xz was > between 2x and 6x slower. Is that the current number?
Here are the numbers, of decompressing alone (rather than, say, a
debootstrap run). User times only, best of three tries.
size amd64 armel
a 99MB unstripped executable
gzip [-6] 38070471 0.75 10.51
gzip -9 37985726 0.74 10.41
xz -0 30007128 2.34 20.10
xz -2 24861804 1.92 17.39
xz [-6] 21921888 1.84 16.82
xz -9 21026804 1.77 16.23
25MB of /dev/urandom
gzip [-6] 26218418 0.11 3.25
gzip -9 26218418 0.12 3.27
xz -0 26215764 0.02 0.43
xz -2 26215764 0.02 0.59
xz [-6] 26215760 0.02 0.47
xz -9 26215760 0.01 0.51
100MB of /dev/zero
gzip [-6] 101791 0.40 4.74
gzip -9 101791 0.39 4.69
xz -0 15388 0.31 3.82
xz -2 15388 0.31 4.07
xz [-6] 15388 0.31 4.03
xz -9 15388 0.33 4.01
There are two interesting pieces here:
* higher compression settings tend to improve speed (I suspected the
opposite...)
* xz seems to have a special case for incompressible data
> It would be useful to have some real-world installation time benchmarks
> with and without xz.
It is said that decompression is a small part of install time, I did not
test that.
>
> BTW, when we switched to building udebx with xz, Philipp Kern benchmarked
> it using little or no additional CPU to decompress xz produced with
> -Zxz -z1 -Sextreme http://lists.debian.org/debian-boot/2011/10/msg00247.html
Per the above, you'd want a higher setting than -1. With the default (-6),
you need just 10MB memory to decompress.
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