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RZIP

rzip is a compression program, similar in functionality to gzip or bzip2, but
able to take advantage long distance redundencies in files, which can sometimes
allow rzip to produce much better compression ratios than other programs. The
original idea behind rzip is described in my PhD thesis (see
http://samba.org/~tridge/), but the implementation in this version is
considerably improved from the original implementation. The new version is much
faster and also produces a better compression ratio.


LATEST RELEASE

The latest release is rzip 2.1. Changes in this release include:
 * Added -L compression level option
 * minor portability fixes
 * fixed a bug that could cause some files to not be able to be uncompressed

You can get this release from the download directory


ADVANTAGES

The principal advantage of rzip is that it has an effective history buffer of
900 Mbyte. This means it can find matching pieces of the input file over huge
distances compared to other commonly used compression programs. The gzip program
by comparison uses a history buffer of 32 kbyte and bzip2 uses a history buffer
of 900 kbyte. The second advantage of rzip over bzip2 is that it is usually
faster. This may seem surprising at first given that rzip uses the bzip2 library
as a backend (for handling the short-range compression), but it makes sense when
you realise that rzip has usually reduced the data a fair bit before handing it
to bzip2, so bzip2 has to do less work.


DISADVANTAGES

rzip is not for everyone! The two biggest disadvantages are that you can't
pipeline rzip (so it can't read from standard input or write to standard
output), and that it uses lots of memory. A typical compression run on a large
file might use a couple of hundred MB of ram. If you have ram to burn and want
the best possible compression rate then rzip is probably for you, otherwise
stick with bzip2 or gzip.


DOCUMENTATION

See the manual page


LICENSE

rzip is released under the GNU General Public License version 2 or later. See
the COPYING file in the source distribution for details.


PERFORMANCE

Compression benchmarks are always tricky things. The existing benchmarks I am
aware of all deal with very small files, and if you are thinking of using rzip
then you are almost certainly not interested in small files! For this reason I
created a new compression corpus in 1998 which I called the "large-corpus". Of
course, typical file sizes are getting bigger all the time, so the term "large"
may not be all that appropriate any more, but it certainly has much larger files
than the commonly used compression corpuses.

You can get a copy of the large-corpus files from
http://samba.org/ftp/tridge/large-corpus/.

In the following I show the compression ratios of the large-corpus for rzip 2.0,
gzip 1.3.5 and bzip2 1.0.2 on my Debian Linux laptop. In all cases the programs
were run with their maximum compresion options.



File Namerzipgzipbzip2 large-corpus/archive 6.03 3.64 4.97 large-corpus/emacs
5.08 3.66 4.62 large-corpus/linux 5.54 4.24 5.23 large-corpus/samba 9.55 3.50
4.78 large-corpus/spamfile29.95 8.4314.23




RELATED PROGRAMS

Con Kolivas has released a very interesting varient of rzip, called lrzip, which
can use multiple compressor backends and achieve even better compression


AUTHORS

The original author of rzip is Andrew Tridgell. Version 2 of rzip also contains
a lot of work from Paul Russell.


DOWNLOAD

You can download the latest release from the download directory.

For the bleeding edge, you can fetch rzip via CVS or rsync. To fetch via cvs use
the following command:

  cvs -d :pserver:cvs@pserver.samba.org:/cvsroot co rzip


To fetch via rsync use this command:

  rsync -Pavz samba.org::ftp/unpacked/rzip .


--------------------------------------------------------------------------------

Andrew Tridgell
rzip AT tridgell.net