feature request: lzma compresion (7zip)

Matthias Schniedermeyer ms at citd.de
Mon Jun 21 02:53:21 MDT 2010

On 17.06.2010 15:37, super master wrote:
> Hello,
> many linux SW is starting to implement new lzma compresson instrad of old zlib (gzip) od bzip2.
> lzma is default comrpession in very good compression SW 7-zip, which is faster and have higher compression ratio then bzip2 or rar.
> Currently its probalby the best compressor in therms of compression and decompression speed / compression ratio.
> In linux there is GNU lzma SW which implements lzma algorithm.
> In my optinion it would be very useful if rsync could use this compressor optionaly as upgrade of old zlib.
> more info: http://en.wikipedia.org/wiki/Lempel%E2%80%93Ziv%E2%80%93Markov_chain_algorithm

lzma draws most of it's strength from using a much larger "Working 
Window" (megabyte to gigabyte, instead of a few kilobyte like gzip).

AFAIU rsync works with blocks in the kilobyte-range, which effectivly 
prevents lzma from using it's main strength.

For illustration i've just tried "xz -0" on a linux-kernel tar-ball.
"xz -0" still uses a much larger window that gzip! The man-page says 
about 6 megabytes and the man-page reserves a future change to an 
algorithm other than lzma.

On said linux-kernel tar-ball the compression was only slightly better 
that gzip.

87634801 byte for gzip with defaults
86841598 byte for gzip -9
85544824 byte for xz -0

For comparison:
55044372 byte for xz -e9

Bis denn

Real Programmers consider "what you see is what you get" to be just as 
bad a concept in Text Editors as it is in women. No, the Real Programmer
wants a "you asked for it, you got it" text editor -- complicated, 
cryptic, powerful, unforgiving, dangerous.

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