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INFO-DIR-SECTION Data Compression
START-INFO-DIR-ENTRY
* Plzip: (plzip).               Parallel compressor compatible with lzip
END-INFO-DIR-ENTRY


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Plzip Manual
************

This manual is for Plzip (version 0.7, 3 December 2010).

* 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


   Copyright (C) 2009, 2010 Antonio Diaz Diaz.

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


File: plzip.info,  Node: Introduction,  Next: Invoking Plzip,  Prev: Top,  Up: Top

1 Introduction
**************

Plzip is a massively parallel (multi-threaded), lossless data compressor
based on the lzlib compression library, with very safe integrity
checking and a user interface similar to the one of bzip2, gzip or lzip.
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 `--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:

filename.lz    becomes   filename
filename.tlz   becomes   filename.tar
anyothername   becomes   anyothername.out

   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.


File: plzip.info,  Node: Invoking Plzip,  Next: Program Design,  Prev: Introduction,  Up: Top

2 Invoking Plzip
****************

The format for running plzip is:

     plzip [OPTIONS] [FILES]

   Plzip supports the following options:

`-h'
`--help'
     Print an informative help message describing the options and exit.

`-V'
`--version'
     Print the version number of plzip on the standard output and exit.

`-B'
`--data-size=SIZE'
     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.

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

`-d'
`--decompress'
     Decompress.

`-f'
`--force'
     Force overwrite of output file.

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

`-m LENGTH'
`--match-length=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.

`-n THREADS'
`--threads=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.

`-o FILE'
`--output=FILE'
     When reading from standard input and `--stdout' has not been
     specified, use `FILE' as the virtual name of the uncompressed
     file. This produces a file named `FILE' when decompressing, and a
     file named `FILE.lz' when compressing.

`-q'
`--quiet'
     Quiet operation. Suppress all messages.

`-s SIZE'
`--dictionary-size=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.

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

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

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

     The bidimensional parameter space of LZMA can't be mapped to a
     linear scale optimal for all files. If your files are large, very
     repetitive, etc, you may need to use the `--match-length' and
     `--dictionary-size' options directly to achieve optimal
     performance.

     Level   Dictionary size   Match length limit
     -1      1 MiB             5 bytes
     -2      1.5 MiB           6 bytes
     -3      2 MiB             8 bytes
     -4      3 MiB             12 bytes
     -5      4 MiB             20 bytes
     -6      8 MiB             36 bytes
     -7      16 MiB            68 bytes
     -8      24 MiB            132 bytes
     -9      32 MiB            273 bytes

`--fast'
`--best'
     Aliases for GNU gzip compatibility.



   Numbers given as arguments to options may be followed by a multiplier
and an optional `B' for "byte".

   Table of SI and binary prefixes (unit multipliers):

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


File: plzip.info,  Node: Program Design,  Next: File Format,  Prev: Invoking Plzip,  Up: Top

3 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.


File: plzip.info,  Node: File Format,  Next: Problems,  Prev: Program Design,  Up: Top

4 File Format
*************

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

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

   represents a variable number of bytes.


   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:
+--+--+--+--+----+----+=============+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ID string | VN | DS | Lzma stream | CRC32 |   Data size   |  Member size  |
+--+--+--+--+----+----+=============+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   All multibyte values are stored in little endian order.

`ID string'
     A four byte string, identifying the member type, with the value
     "LZIP".

`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
     `Member size'.

`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.

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

`CRC32 (4 bytes)'
     CRC of the uncompressed original data.

`Data size (8 bytes)'
     Size of the uncompressed original data.

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



File: plzip.info,  Node: Problems,  Next: Concept Index,  Prev: File Format,  Up: Top

5 Reporting Bugs
****************

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
<lzip-bug@nongnu.org>. Include the version number, which you can find
by running `plzip --version'.


File: plzip.info,  Node: Concept Index,  Prev: Problems,  Up: Top

Concept Index
*************

[index]
* Menu:

* bugs:                                  Problems.              (line 6)
* file format:                           File Format.           (line 6)
* getting help:                          Problems.              (line 6)
* introduction:                          Introduction.          (line 6)
* invoking:                              Invoking Plzip.        (line 6)
* options:                               Invoking Plzip.        (line 6)
* program design:                        Program Design.        (line 6)
* usage:                                 Invoking Plzip.        (line 6)
* version:                               Invoking Plzip.        (line 6)



Tag Table:
Node: Top223
Node: Introduction833
Node: Invoking Plzip3592
Node: Program Design7840
Node: File Format8502
Node: Problems10458
Node: Concept Index10987

End Tag Table