path: root/doc/plzip.texinfo

\input texinfo @c -*-texinfo-*-
@c %**start of header
@setfilename plzip.info
@settitle Plzip Manual
@finalout
@c %**end of header

@set UPDATED 20 March 2010
@set VERSION 0.6

@dircategory Data Compression
@direntry
* Plzip: (plzip).               Parallel compressor compatible with lzip
@end direntry


@titlepage
@title Plzip
@subtitle A data compressor based on the LZMA algorithm
@subtitle for Plzip version @value{VERSION}, @value{UPDATED}
@author by Antonio Diaz Diaz

@page
@vskip 0pt plus 1filll
@end titlepage

@contents

@node Top
@top

This manual is for Plzip (version @value{VERSION}, @value{UPDATED}).

@menu
* Introduction::	Purpose and features of plzip
* Invoking Plzip::	Command line interface
* Program Design::	Internal structure of plzip
* File Format::		Detailed format of the compressed file
* Problems::		Reporting bugs
* Concept Index::	Index of concepts
@end menu

@sp 1
Copyright @copyright{} 2009, 2010 Antonio Diaz Diaz.

This manual is free documentation: you have unlimited permission
to copy, distribute and modify it.


@node Introduction
@chapter Introduction
@cindex introduction

Plzip is a massively parallel (multi-threaded), lossless data compressor
based on the LZMA algorithm, with very safe integrity checking and a
user interface similar to the one of gzip or bzip2. Plzip uses the lzip
file format; the files produced by plzip are fully compatible with
lzip-1.4 or newer.

Plzip is intended for faster compression/decompression of big files on
multiprocessor machines, which makes it specially well suited for
distribution of big software files and large scale data archiving. On
files big enough, plzip can use hundreds of processors.

Plzip replaces every file given in the command line with a compressed
version of itself, with the name "original_name.lz". Each compressed
file has the same modification date, permissions, and, when possible,
ownership as the corresponding original, so that these properties can be
correctly restored at decompression time. Plzip is able to read from some
types of non regular files if the @samp{--stdout} option is specified.

If no file names are specified, plzip compresses (or decompresses) from
standard input to standard output. In this case, plzip will decline to
write compressed output to a terminal, as this would be entirely
incomprehensible and therefore pointless.

Plzip will correctly decompress a file which is the concatenation of two
or more compressed files. The result is the concatenation of the
corresponding uncompressed files. Integrity testing of concatenated
compressed files is also supported.

When decompressing, plzip attempts to guess the name for the decompressed
file from that of the compressed file as follows:

@multitable {anyothername} {becomes} {anyothername.out}
@item filename.lz  @tab becomes @tab filename
@item filename.tlz @tab becomes @tab filename.tar
@item anyothername @tab becomes @tab anyothername.out
@end multitable

As a self-check for your protection, plzip stores in the member trailer
the 32-bit CRC of the original data and the size of the original data,
to make sure that the decompressed version of the data is identical to
the original. This guards against corruption of the compressed data, and
against undetected bugs in plzip (hopefully very unlikely). The chances
of data corruption going undetected are microscopic, less than one
chance in 4000 million for each member processed. Be aware, though, that
the check occurs upon decompression, so it can only tell you that
something is wrong. It can't help you recover the original uncompressed
data.

Return values: 0 for a normal exit, 1 for environmental problems (file
not found, invalid flags, I/O errors, etc), 2 to indicate a corrupt or
invalid input file, 3 for an internal consistency error (eg, bug) which
caused plzip to panic.


@node Invoking Plzip
@chapter Invoking Plzip
@cindex invoking
@cindex options
@cindex usage
@cindex version

The format for running plzip is:

@example
plzip [@var{options}] [@var{files}]
@end example

Plzip supports the following options:

@table @samp
@item --help
@itemx -h
Print an informative help message describing the options and exit.

@item --version
@itemx -V
Print the version number of plzip on the standard output and exit.

@item --data-size=@var{size}
@itemx -B
Set the input data block size in bytes. The input file will be divided
in chunks of this size before compression is performed. Valid values
range from 8KiB to 1GiB. Default value is two times the dictionary size.
Plzip will reduce the dictionary size if it is larger than the chosen
data size.

@item --stdout
@itemx -c
Compress or decompress to standard output. Needed when reading from a
named pipe (fifo) or from a device.

@item --decompress
@itemx -d
Decompress.

@item --force
@itemx -f
Force overwrite of output file.

@item --keep
@itemx -k
Keep (don't delete) input files during compression or decompression.

@item --match-length=@var{length}
@itemx -m @var{length}
Set the match length limit in bytes. Valid values range from 5 to 273.
Larger values usually give better compression ratios but longer
compression times.

@item --threads=@var{threads}
@itemx -n @var{threads}
Set the number of worker threads. Valid values range from 1 to "as many
as your system can support". If this option is not used, plzip tries to
detect the number of processors in the system and use it as default
value.

@item --output=@var{file}
@itemx -o @var{file}
When reading from standard input and @samp{--stdout} has not been
specified, use @samp{@var{file}} as the virtual name of the uncompressed
file. This produces a file named @samp{@var{file}} when decompressing,
and a file named @samp{@var{file}.lz} when compressing.

@item --quiet
@itemx -q
Quiet operation. Suppress all messages.

@item --dictionary-size=@var{size}
@itemx -s @var{size}
Set the dictionary size limit in bytes. Valid values range from 4KiB to
512MiB. Note that dictionary sizes are quantized. If the specified size
does not match one of the valid sizes, it will be rounded upwards.

@item --test
@itemx -t
Check integrity of the specified file(s), but don't decompress them.
This really performs a trial decompression and throws away the result.
Use @samp{-tvv} or @samp{-tvvv} to see information about the file.

@item --verbose
@itemx -v
Verbose mode. Show the compression ratio for each file processed.
Further -v's increase the verbosity level.

@item -1 .. -9
Set the compression parameters (dictionary size and match length limit)
as shown in the table below. Note that @samp{-9} can be much slower than
@samp{-1}. These options have no effect when decompressing.

@multitable {Level} {Dictionary size} {Match length limit}
@item Level @tab Dictionary size @tab Match length limit
@item -1 @tab  1 MiB @tab  10 bytes
@item -2 @tab  1.5 MiB @tab  12 bytes
@item -3 @tab  2 MiB @tab  17 bytes
@item -4 @tab  3 MiB @tab  26 bytes
@item -5 @tab  4 MiB @tab  44 bytes
@item -6 @tab  8 MiB @tab  80 bytes
@item -7 @tab 16 MiB @tab 108 bytes
@item -8 @tab 24 MiB @tab 163 bytes
@item -9 @tab 32 MiB @tab 273 bytes
@end multitable

@item --fast
@itemx --best
Aliases for GNU gzip compatibility.

@end table

@sp 1
Numbers given as arguments to options may be followed by a multiplier
and an optional @samp{B} for "byte".

Table of SI and binary prefixes (unit multipliers):

@multitable {Prefix} {kilobyte  (10^3 = 1000)} {|} {Prefix} {kibibyte (2^10 = 1024)}
@item Prefix @tab Value               @tab | @tab Prefix @tab Value
@item k @tab kilobyte  (10^3 = 1000)  @tab | @tab Ki @tab kibibyte (2^10 = 1024)
@item M @tab megabyte  (10^6)         @tab | @tab Mi @tab mebibyte (2^20)
@item G @tab gigabyte  (10^9)         @tab | @tab Gi @tab gibibyte (2^30)
@item T @tab terabyte  (10^12)        @tab | @tab Ti @tab tebibyte (2^40)
@item P @tab petabyte  (10^15)        @tab | @tab Pi @tab pebibyte (2^50)
@item E @tab exabyte   (10^18)        @tab | @tab Ei @tab exbibyte (2^60)
@item Z @tab zettabyte (10^21)        @tab | @tab Zi @tab zebibyte (2^70)
@item Y @tab yottabyte (10^24)        @tab | @tab Yi @tab yobibyte (2^80)
@end multitable


@node Program Design
@chapter Program Design
@cindex program design

For each input file, a splitter thread and several worker threads are
created, acting the main thread as muxer (multiplexer) thread. A "packet
courier" takes care of data transfers among threads and limits the
maximum number of data blocks (packets) being processed simultaneously.

The splitter reads data blocks from the input file, and distributes them
to the workers. The workers (de)compress the blocks received from the
splitter. The muxer collects processed packets from the workers, and
writes them to the output file.


@node File Format
@chapter File Format
@cindex file format

In the diagram below, a box like this:
@verbatim
+---+
|   | <-- the vertical bars might be missing
+---+
@end verbatim

represents one byte; a box like this:
@verbatim
+==============+
|              |
+==============+
@end verbatim

represents a variable number of bytes.

@sp 1
A lzip file consists of a series of "members" (compressed data sets).
The members simply appear one after another in the file, with no
additional information before, between, or after them.

Each member has the following structure:
@verbatim
+--+--+--+--+----+----+=============+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ID string | VN | DS | Lzma stream | CRC32 |   Data size   |  Member size  |
+--+--+--+--+----+----+=============+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
@end verbatim

All multibyte values are stored in little endian order.

@table @samp
@item ID string
A four byte string, identifying the member type, with the value "LZIP".

@item VN (version number, 1 byte)
Just in case something needs to be modified in the future. Valid values
are 0 and 1. Version 0 files have only one member and lack @samp{Member
size}.

@item DS (coded dictionary size, 1 byte)
Bits 4-0 contain the base 2 logarithm of the base dictionary size.@*
Bits 7-5 contain the number of "wedges" to substract from the base
dictionary size to obtain the dictionary size. The size of a wedge is
(base dictionary size / 16).@*
Valid values for dictionary size range from 4KiB to 512MiB.

@item Lzma stream
The lzma stream, finished by an end of stream marker. Uses default values
for encoder properties.

@item CRC32 (4 bytes)
CRC of the uncompressed original data.

@item Data size (8 bytes)
Size of the uncompressed original data.

@item Member size (8 bytes)
Total size of the member, including header and trailer. This facilitates
safe recovery of undamaged members from multimember files.

@end table


@node Problems
@chapter Reporting Bugs
@cindex bugs
@cindex getting help

There are probably bugs in plzip. There are certainly errors and
omissions in this manual. If you report them, they will get fixed. If
you don't, no one will ever know about them and they will remain unfixed
for all eternity, if not longer.

If you find a bug in plzip, please send electronic mail to
@email{lzip-bug@@nongnu.org}. Include the version number, which you can
find by running @w{@samp{plzip --version}}.


@node Concept Index
@unnumbered Concept Index

@printindex cp

@bye