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diff --git a/doc/plzip.info b/doc/plzip.info index f8f7e08..2e64673 100644 --- a/doc/plzip.info +++ b/doc/plzip.info @@ -11,7 +11,7 @@ File: plzip.info, Node: Top, Next: Introduction, Up: (dir) Plzip Manual ************ -This manual is for Plzip (version 1.2, 29 August 2014). +This manual is for Plzip (version 1.3-pre1, 25 November 2014). * Menu: @@ -19,6 +19,8 @@ This manual is for Plzip (version 1.2, 29 August 2014). * Program design:: Internal structure of plzip * Invoking plzip:: Command line interface * File format:: Detailed format of the compressed file +* Memory requirements:: Memory required to compress and decompress +* Minimum file sizes:: Minimum file sizes required for full speed * Problems:: Reporting bugs * Concept index:: Index of concepts @@ -40,16 +42,18 @@ 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; -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 (0.4 to 2 percent larger compressed files). 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 (*note Minimum file sizes::). 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. - The lzip file format is designed for long-term data archiving, taking -into account both data integrity and decoder availability: + The lzip file format is designed for data sharing and long-term +archiving, taking into account both data integrity and decoder +availability: * The lzip format provides very safe integrity checking and some data recovery means. The lziprecover program can repair bit-flip errors @@ -64,50 +68,23 @@ into account both data integrity and decoder availability: archaeologist to extract the data from a lzip file long after quantum computers eventually render LZMA obsolete. - * Additionally lzip is copylefted, which guarantees that it will - remain free forever. + * Additionally the lzip reference implementation 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. - The member trailer stores the 32-bit CRC of the original data, the -size of the original data and the size of the member. These values, -together with the value remaining in the range decoder and the -end-of-stream marker, provide a 4 factor integrity checking which -guarantees 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. 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. - 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 other programs like tar or zutils. - The amount of memory required *per thread* is approximately the -following: - - * For compression; 3 times the data size (*note --data-size::) plus - 11 times the dictionary size. - - * For decompression or testing of a non-seekable file or of standard - input; 2 times the dictionary size plus up to 32 MiB. - - * For decompression of a regular file to a non-seekable file or to - standard output; the dictionary size plus up to 32 MiB. - - * For decompression of a regular file to another regular file, or for - testing of a regular file; the dictionary size. - Plzip will automatically use the smallest possible dictionary size for each file without exceeding the given limit. Keep in mind that the decompression memory requirement is affected at compression time by the -choice of dictionary size limit. +choice of dictionary size limit (*note Memory requirements::). When compressing, plzip replaces every file given in the command line with a compressed version of itself, with the name "original_name.lz". @@ -245,8 +222,8 @@ The format for running plzip is: value. Note that the number of usable threads is limited to - ceil( file_size / data_size ) during compression (*note - --data-size::), and to the number of members in the input during + ceil( file_size / data_size ) during compression (*note Minimum + file sizes::), and to the number of members in the input during decompression. '-o FILE' @@ -287,8 +264,8 @@ The format for running plzip is: When compressing, show the compression ratio for each file processed. A second '-v' shows the progress of compression. When decompressing or testing, further -v's (up to 4) increase the - verbosity level, showing status, compression ratio, decompressed - size, and compressed size. + verbosity level, showing status, compression ratio, dictionary + size, decompressed size, and compressed size. '-1 .. -9' Set the compression parameters (dictionary size and match length @@ -299,8 +276,7 @@ The format for running plzip is: 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. For example, '-9m64' usually compresses executables - more (and faster) than '-9'. + performance. Level Dictionary size Match length limit -1 1 MiB 5 bytes @@ -340,7 +316,7 @@ invalid input file, 3 for an internal consistency error (eg, bug) which caused plzip to panic. -File: plzip.info, Node: File format, Next: Problems, Prev: Invoking plzip, Up: Top +File: plzip.info, Node: File format, Next: Memory requirements, Prev: Invoking plzip, Up: Top 4 File format ************* @@ -413,9 +389,70 @@ additional information before, between, or after them. -File: plzip.info, Node: Problems, Next: Concept index, Prev: File format, Up: Top +File: plzip.info, Node: Memory requirements, Next: Minimum file sizes, Prev: File format, Up: Top + +5 Memory required to compress and decompress +******************************************** + +The amount of memory required *per thread* is approximately the +following: + + * For compression; 11 times the dictionary size plus 3 times the + data size (*note --data-size::). + + * For decompression of a regular (seekable) file to another regular + file, or for testing of a regular file; the dictionary size. Note + that regular files with more than 1024 bytes of trailing garbage + are treated as non-seekable. + + * For testing of a non-seekable file or of standard input; the + dictionary size plus up to 5 MiB. + + * For decompression of a regular file to a non-seekable file or to + standard output; the dictionary size plus up to 32 MiB. + + * For decompression of a non-seekable file or of standard input; the + dictionary size plus up to 35 MiB. + + +File: plzip.info, Node: Minimum file sizes, Next: Problems, Prev: Memory requirements, Up: Top + +6 Minimum file sizes required for full compression speed +******************************************************** + +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. + + For this to work as expected (and roughly multiply the compression +speed by the number of available processors), the uncompressed file +must be at least as large as the number of worker threads times the +chunk size (*note --data-size::). Else some processors will not get any +data to compress, and compression will be proportionally slower. The +maximum speed increase achievable on a given file is limited by the +ratio (file_size / data_size). + + The following table shows the minimum uncompressed file size needed +for full use of N processors at a given compression level, using the +default data size for each level: + +Processors 2 3 4 8 16 64 +------------------------------------------------------------------------- +Level +-1 4 MiB 6 MiB 8 MiB 16 MiB 32 MiB 128 MiB +-2 6 MiB 9 MiB 12 MiB 24 MiB 48 MiB 192 MiB +-3 8 MiB 12 MiB 16 MiB 32 MiB 64 MiB 256 MiB +-4 12 MiB 18 MiB 24 MiB 48 MiB 96 MiB 384 MiB +-5 16 MiB 24 MiB 32 MiB 64 MiB 128 MiB 512 MiB +-6 32 MiB 48 MiB 64 MiB 128 MiB 256 MiB 1 GiB +-7 64 MiB 96 MiB 128 MiB 256 MiB 512 MiB 2 GiB +-8 96 MiB 144 MiB 192 MiB 384 MiB 768 MiB 3 GiB +-9 128 MiB 192 MiB 256 MiB 512 MiB 1 GiB 4 GiB + + +File: plzip.info, Node: Problems, Next: Concept index, Prev: Minimum file sizes, Up: Top -5 Reporting bugs +7 Reporting bugs **************** There are probably bugs in plzip. There are certainly errors and @@ -441,6 +478,8 @@ Concept index * getting help: Problems. (line 6) * introduction: Introduction. (line 6) * invoking: Invoking plzip. (line 6) +* memory requirements: Memory requirements. (line 6) +* minimum file sizes: Minimum file sizes. (line 6) * options: Invoking plzip. (line 6) * program design: Program design. (line 6) * usage: Invoking plzip. (line 6) @@ -450,13 +489,15 @@ Concept index Tag Table: Node: Top221 -Node: Introduction847 -Node: Program design6279 -Node: Invoking plzip7868 -Ref: --data-size8313 -Node: File format13471 -Node: Problems15976 -Node: Concept index16505 +Node: Introduction994 +Node: Program design5290 +Node: Invoking plzip6879 +Ref: --data-size7324 +Node: File format12420 +Node: Memory requirements14936 +Node: Minimum file sizes15913 +Node: Problems17765 +Node: Concept index18301 End Tag Table |