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@@ -1,14 +1,24 @@ Description -Plzip is a massively parallel (multi-threaded), lossless data compressor +Plzip is a massively parallel (multi-threaded) lossless data compressor based on the lzlib compression library, with a user interface similar to the one of lzip, bzip2 or gzip. Plzip can compress/decompress large files on multiprocessor machines much faster than lzip, at the cost of a slightly reduced compression -ratio. Note that the number of usable threads is limited by file size, -so on files larger than a few GB plzip can use hundreds of processors, -but on files of only a few MB plzip is no faster than lzip. +ratio. Note that the number of usable threads is limited by file size; +on files larger than a few GB plzip can use hundreds of processors, but +on files of only a few MB plzip is no faster than lzip. + +When compressing, plzip divides the input file into chunks and +compresses as many chunks simultaneously as worker threads are chosen, +creating a multi-member compressed file. + +When decompressing, plzip decompresses as many members simultaneously as +worker threads are chosen. Files that were compressed with lzip will not +be decompressed faster than using lzip (unless the "-b" option was used) +because lzip usually produces single-member files, which can't be +decompressed in parallel. Plzip uses the lzip file format; the files produced by plzip are fully compatible with lzip-1.4 or newer, and can be rescued with lziprecover. @@ -32,9 +42,15 @@ into account both data integrity and decoder availability: * Additionally lzip is copylefted, which guarantees that it will remain free forever. +A nice feature of the lzip format is that a corrupt byte is easier to +repair the nearer it is from the beginning of the file. Therefore, with +the help of lziprecover, losing an entire archive just because of a +corrupt byte near the beginning is a thing of the past. + Plzip uses the same well-defined exit status values used by lzip and bzip2, which makes it safer than compressors returning ambiguous warning -values (like gzip) when it is used as a back end for tar or zutils. +values (like gzip) when it is used as a back end for other programs like +tar or zutils. Plzip will automatically use the smallest possible dictionary size for each file without exceeding the given limit. Keep in mind that the @@ -70,7 +86,7 @@ corresponding uncompressed files. Integrity testing of concatenated compressed files is also supported. -Copyright (C) 2009, 2010, 2011, 2012, 2013, 2014 Antonio Diaz Diaz. +Copyright (C) 2009-2014 Antonio Diaz Diaz. This file is free documentation: you have unlimited permission to copy, distribute and modify it. |