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make man
This commit is contained in:
W. Felix Handte
parent
382026f096
commit
11aba9b316
115
programs/zstd.1
115
programs/zstd.1
@ -1,5 +1,5 @@
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.
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.TH "ZSTD" "1" "August 2022" "zstd 1.5.3" "User Commands"
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.TH "ZSTD" "1" "December 2022" "zstd 1.5.3" "User Commands"
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.
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.SH "NAME"
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\fBzstd\fR \- zstd, zstdmt, unzstd, zstdcat \- Compress or decompress \.zst files
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@ -17,10 +17,10 @@
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\fBzstdcat\fR is equivalent to \fBzstd \-dcf\fR
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.
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.SH "DESCRIPTION"
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\fBzstd\fR is a fast lossless compression algorithm and data compression tool, with command line syntax similar to \fBgzip (1)\fR and \fBxz (1)\fR\. It is based on the \fBLZ77\fR family, with further FSE & huff0 entropy stages\. \fBzstd\fR offers highly configurable compression speed, from fast modes at > 200 MB/s per core, to strong modes with excellent compression ratios\. It also features a very fast decoder, with speeds > 500 MB/s per core\.
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\fBzstd\fR is a fast lossless compression algorithm and data compression tool, with command line syntax similar to \fBgzip\fR(1) and \fBxz\fR(1)\. It is based on the \fBLZ77\fR family, with further FSE & huff0 entropy stages\. \fBzstd\fR offers highly configurable compression speed, from fast modes at > 200 MB/s per core, to strong modes with excellent compression ratios\. It also features a very fast decoder, with speeds > 500 MB/s per core\.
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.
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.P
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\fBzstd\fR command line syntax is generally similar to gzip, but features the following differences :
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\fBzstd\fR command line syntax is generally similar to gzip, but features the following differences:
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.
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.IP "\(bu" 4
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Source files are preserved by default\. It\'s possible to remove them automatically by using the \fB\-\-rm\fR command\.
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@ -34,10 +34,13 @@ When compressing a single file, \fBzstd\fR displays progress notifications and r
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.IP "\(bu" 4
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\fBzstd\fR does not accept input from console, though it does accept \fBstdin\fR when it\'s not the console\.
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.
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.IP "\(bu" 4
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\fBzstd\fR does not store the input\'s filename or attributes, only its contents\.
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.
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.IP "" 0
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.
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.P
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\fBzstd\fR processes each \fIfile\fR according to the selected operation mode\. If no \fIfiles\fR are given or \fIfile\fR is \fB\-\fR, \fBzstd\fR reads from standard input and writes the processed data to standard output\. \fBzstd\fR will refuse to write compressed data to standard output if it is a terminal : it will display an error message and skip the \fIfile\fR\. Similarly, \fBzstd\fR will refuse to read compressed data from standard input if it is a terminal\.
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\fBzstd\fR processes each \fIfile\fR according to the selected operation mode\. If no \fIfiles\fR are given or \fIfile\fR is \fB\-\fR, \fBzstd\fR reads from standard input and writes the processed data to standard output\. \fBzstd\fR will refuse to write compressed data to standard output if it is a terminal: it will display an error message and skip the file\. Similarly, \fBzstd\fR will refuse to read compressed data from standard input if it is a terminal\.
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.
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.P
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Unless \fB\-\-stdout\fR or \fB\-o\fR is specified, \fIfiles\fR are written to a new file whose name is derived from the source \fIfile\fR name:
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@ -50,12 +53,12 @@ When decompressing, the \fB\.zst\fR suffix is removed from the source filename t
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.
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.IP "" 0
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.
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.SS "Concatenation with \.zst files"
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.SS "Concatenation with \.zst Files"
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It is possible to concatenate multiple \fB\.zst\fR files\. \fBzstd\fR will decompress such agglomerated file as if it was a single \fB\.zst\fR file\.
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.
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.SH "OPTIONS"
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.
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.SS "Integer suffixes and special values"
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.SS "Integer Suffixes and Special Values"
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In most places where an integer argument is expected, an optional suffix is supported to easily indicate large integers\. There must be no space between the integer and the suffix\.
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.
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.TP
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@ -66,7 +69,7 @@ Multiply the integer by 1,024 (2^10)\. \fBKi\fR, \fBK\fR, and \fBKB\fR are accep
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\fBMiB\fR
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Multiply the integer by 1,048,576 (2^20)\. \fBMi\fR, \fBM\fR, and \fBMB\fR are accepted as synonyms for \fBMiB\fR\.
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.
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.SS "Operation mode"
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.SS "Operation Mode"
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If multiple operation mode options are given, the last one takes effect\.
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.
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.TP
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@ -83,20 +86,20 @@ Test the integrity of compressed \fIfiles\fR\. This option is equivalent to \fB\
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.
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.TP
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\fB\-b#\fR
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Benchmark file(s) using compression level #
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Benchmark file(s) using compression level \fI#\fR\. See \fIBENCHMARK\fR below for a description of this operation\.
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.
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.TP
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\fB\-\-train FILEs\fR
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Use FILEs as a training set to create a dictionary\. The training set should contain a lot of small files (> 100)\.
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\fB\-\-train FILES\fR
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Use \fIFILES\fR as a training set to create a dictionary\. The training set should contain a lot of small files (> 100)\. See \fIDICTIONARY BUILDER\fR below for a description of this operation\.
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.
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.TP
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\fB\-l\fR, \fB\-\-list\fR
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Display information related to a zstd compressed file, such as size, ratio, and checksum\. Some of these fields may not be available\. This command\'s output can be augmented with the \fB\-v\fR modifier\.
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.
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.SS "Operation modifiers"
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.SS "Operation Modifiers"
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.
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.IP "\(bu" 4
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\fB\-#\fR: \fB#\fR compression level [1\-19] (default: 3)
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\fB\-#\fR: selects \fB#\fR compression level [1\-19] (default: 3)
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.
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.IP "\(bu" 4
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\fB\-\-ultra\fR: unlocks high compression levels 20+ (maximum 22), using a lot more memory\. Note that decompression will also require more memory when using these levels\.
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@ -108,13 +111,22 @@ Display information related to a zstd compressed file, such as size, ratio, and
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\fB\-T#\fR, \fB\-\-threads=#\fR: Compress using \fB#\fR working threads (default: 1)\. If \fB#\fR is 0, attempt to detect and use the number of physical CPU cores\. In all cases, the nb of threads is capped to \fBZSTDMT_NBWORKERS_MAX\fR, which is either 64 in 32\-bit mode, or 256 for 64\-bit environments\. This modifier does nothing if \fBzstd\fR is compiled without multithread support\.
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.
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.IP "\(bu" 4
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\fB\-\-single\-thread\fR: Use a single thread for both I/O and compression\. As compression is serialized with I/O, this can be slightly slower\. Single\-thread mode features significantly lower memory usage, which can be useful for systems with limited amount of memory, such as 32\-bit systems\. Note 1 : this mode is the only available one when multithread support is disabled\. Note 2 : this mode is different from \fB\-T1\fR, which spawns 1 compression thread in parallel with I/O\. Final compressed result is also slightly different from \fB\-T1\fR\.
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\fB\-\-single\-thread\fR: Use a single thread for both I/O and compression\. As compression is serialized with I/O, this can be slightly slower\. Single\-thread mode features significantly lower memory usage, which can be useful for systems with limited amount of memory, such as 32\-bit systems\.
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.
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.IP
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Note 1: this mode is the only available one when multithread support is disabled\.
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.
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.IP
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Note 2: this mode is different from \fB\-T1\fR, which spawns 1 compression thread in parallel with I/O\. Final compressed result is also slightly different from \fB\-T1\fR\.
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.
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.IP "\(bu" 4
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\fB\-\-auto\-threads={physical,logical} (default: physical)\fR: When using a default amount of threads via \fB\-T0\fR, choose the default based on the number of detected physical or logical cores\.
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.
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.IP "\(bu" 4
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\fB\-\-adapt[=min=#,max=#]\fR : \fBzstd\fR will dynamically adapt compression level to perceived I/O conditions\. Compression level adaptation can be observed live by using command \fB\-v\fR\. Adaptation can be constrained between supplied \fBmin\fR and \fBmax\fR levels\. The feature works when combined with multi\-threading and \fB\-\-long\fR mode\. It does not work with \fB\-\-single\-thread\fR\. It sets window size to 8 MB by default (can be changed manually, see \fBwlog\fR)\. Due to the chaotic nature of dynamic adaptation, compressed result is not reproducible\. \fInote\fR : at the time of this writing, \fB\-\-adapt\fR can remain stuck at low speed when combined with multiple worker threads (>=2)\.
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\fB\-\-adapt[=min=#,max=#]\fR: \fBzstd\fR will dynamically adapt compression level to perceived I/O conditions\. Compression level adaptation can be observed live by using command \fB\-v\fR\. Adaptation can be constrained between supplied \fBmin\fR and \fBmax\fR levels\. The feature works when combined with multi\-threading and \fB\-\-long\fR mode\. It does not work with \fB\-\-single\-thread\fR\. It sets window size to 8 MiB by default (can be changed manually, see \fBwlog\fR)\. Due to the chaotic nature of dynamic adaptation, compressed result is not reproducible\.
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.
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.IP
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\fINote\fR: at the time of this writing, \fB\-\-adapt\fR can remain stuck at low speed when combined with multiple worker threads (>=2)\.
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.
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.IP "\(bu" 4
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\fB\-\-long[=#]\fR: enables long distance matching with \fB#\fR \fBwindowLog\fR, if \fB#\fR is not present it defaults to \fB27\fR\. This increases the window size (\fBwindowLog\fR) and memory usage for both the compressor and decompressor\. This setting is designed to improve the compression ratio for files with long matches at a large distance\.
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@ -126,40 +138,49 @@ Note: If \fBwindowLog\fR is set to larger than 27, \fB\-\-long=windowLog\fR or \
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\fB\-D DICT\fR: use \fBDICT\fR as Dictionary to compress or decompress FILE(s)
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.
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.IP "\(bu" 4
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\fB\-\-patch\-from FILE\fR: Specify the file to be used as a reference point for zstd\'s diff engine\. This is effectively dictionary compression with some convenient parameter selection, namely that windowSize > srcSize\.
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\fB\-\-patch\-from FILE\fR: Specify the file to be used as a reference point for zstd\'s diff engine\. This is effectively dictionary compression with some convenient parameter selection, namely that \fIwindowSize\fR > \fIsrcSize\fR\.
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.
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.IP
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Note: cannot use both this and \-D together Note: \fB\-\-long\fR mode will be automatically activated if chainLog < fileLog (fileLog being the windowLog required to cover the whole file)\. You can also manually force it\. Note: for all levels, you can use \-\-patch\-from in \-\-single\-thread mode to improve compression ratio at the cost of speed Note: for level 19, you can get increased compression ratio at the cost of speed by specifying \fB\-\-zstd=targetLength=\fR to be something large (i\.e\. 4096), and by setting a large \fB\-\-zstd=chainLog=\fR
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Note: cannot use both this and \fB\-D\fR together\.
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.
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.IP
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Note: \fB\-\-long\fR mode will be automatically activated if \fIchainLog\fR < \fIfileLog\fR (\fIfileLog\fR being the \fIwindowLog\fR required to cover the whole file)\. You can also manually force it\.
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.
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.IP
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Note: for all levels, you can use \fB\-\-patch\-from\fR in \fB\-\-single\-thread\fR mode to improve compression ratio at the cost of speed\.
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.
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.IP
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Note: for level 19, you can get increased compression ratio at the cost of speed by specifying \fB\-\-zstd=targetLength=\fR to be something large (i\.e\. 4096), and by setting a large \fB\-\-zstd=chainLog=\fR\.
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.
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.IP "\(bu" 4
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\fB\-\-rsyncable\fR : \fBzstd\fR will periodically synchronize the compression state to make the compressed file more rsync\-friendly\. There is a negligible impact to compression ratio, and the faster compression levels will see a small compression speed hit\. This feature does not work with \fB\-\-single\-thread\fR\. You probably don\'t want to use it with long range mode, since it will decrease the effectiveness of the synchronization points, but your mileage may vary\.
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\fB\-\-rsyncable\fR: \fBzstd\fR will periodically synchronize the compression state to make the compressed file more rsync\-friendly\. There is a negligible impact to compression ratio, and the faster compression levels will see a small compression speed hit\. This feature does not work with \fB\-\-single\-thread\fR\. You probably don\'t want to use it with long range mode, since it will decrease the effectiveness of the synchronization points, but your mileage may vary\.
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.
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.IP "\(bu" 4
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\fB\-C\fR, \fB\-\-[no\-]check\fR: add integrity check computed from uncompressed data (default: enabled)
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.
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.IP "\(bu" 4
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\fB\-\-[no\-]content\-size\fR: enable / disable whether or not the original size of the file is placed in the header of the compressed file\. The default option is \-\-content\-size (meaning that the original size will be placed in the header)\.
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\fB\-\-[no\-]content\-size\fR: enable / disable whether or not the original size of the file is placed in the header of the compressed file\. The default option is \fB\-\-content\-size\fR (meaning that the original size will be placed in the header)\.
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.
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.IP "\(bu" 4
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\fB\-\-no\-dictID\fR: do not store dictionary ID within frame header (dictionary compression)\. The decoder will have to rely on implicit knowledge about which dictionary to use, it won\'t be able to check if it\'s correct\.
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.
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.IP "\(bu" 4
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\fB\-M#\fR, \fB\-\-memory=#\fR: Set a memory usage limit\. By default, \fBzstd\fR uses 128 MB for decompression as the maximum amount of memory the decompressor is allowed to use, but you can override this manually if need be in either direction (i\.e\. you can increase or decrease it)\.
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\fB\-M#\fR, \fB\-\-memory=#\fR: Set a memory usage limit\. By default, \fBzstd\fR uses 128 MiB for decompression as the maximum amount of memory the decompressor is allowed to use, but you can override this manually if need be in either direction (i\.e\. you can increase or decrease it)\.
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.
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.IP
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This is also used during compression when using with \-\-patch\-from=\. In this case, this parameter overrides that maximum size allowed for a dictionary\. (128 MB)\.
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This is also used during compression when using with \fB\-\-patch\-from=\fR\. In this case, this parameter overrides that maximum size allowed for a dictionary\. (128 MiB)\.
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.
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.IP
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Additionally, this can be used to limit memory for dictionary training\. This parameter overrides the default limit of 2 GB\. zstd will load training samples up to the memory limit and ignore the rest\.
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Additionally, this can be used to limit memory for dictionary training\. This parameter overrides the default limit of 2 GiB\. zstd will load training samples up to the memory limit and ignore the rest\.
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.
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.IP "\(bu" 4
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\fB\-\-stream\-size=#\fR : Sets the pledged source size of input coming from a stream\. This value must be exact, as it will be included in the produced frame header\. Incorrect stream sizes will cause an error\. This information will be used to better optimize compression parameters, resulting in better and potentially faster compression, especially for smaller source sizes\.
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\fB\-\-stream\-size=#\fR: Sets the pledged source size of input coming from a stream\. This value must be exact, as it will be included in the produced frame header\. Incorrect stream sizes will cause an error\. This information will be used to better optimize compression parameters, resulting in better and potentially faster compression, especially for smaller source sizes\.
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.
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.IP "\(bu" 4
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\fB\-\-size\-hint=#\fR: When handling input from a stream, \fBzstd\fR must guess how large the source size will be when optimizing compression parameters\. If the stream size is relatively small, this guess may be a poor one, resulting in a higher compression ratio than expected\. This feature allows for controlling the guess when needed\. Exact guesses result in better compression ratios\. Overestimates result in slightly degraded compression ratios, while underestimates may result in significant degradation\.
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.
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.IP "\(bu" 4
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\fB\-o FILE\fR: save result into \fBFILE\fR
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\fB\-o FILE\fR: save result into \fBFILE\fR\.
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.
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.IP "\(bu" 4
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\fB\-f\fR, \fB\-\-force\fR: disable input and output checks\. Allows overwriting existing files, input from console, output to stdout, operating on links, block devices, etc\. During decompression and when the output destination is stdout, pass\-through unrecognized formats as\-is\.
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@ -171,10 +192,10 @@ Additionally, this can be used to limit memory for dictionary training\. This pa
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\fB\-\-[no\-]sparse\fR: enable / disable sparse FS support, to make files with many zeroes smaller on disk\. Creating sparse files may save disk space and speed up decompression by reducing the amount of disk I/O\. default: enabled when output is into a file, and disabled when output is stdout\. This setting overrides default and can force sparse mode over stdout\.
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.
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.IP "\(bu" 4
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\fB\-\-[no\-]pass\-through\fR enable / disable passing through uncompressed files as\-is\. During decompression when pass\-through is enabled, unrecognized formats will be copied as\-is from the input to the output\. By default, pass\-through will occur when the output destination is stdout and the force (\-f) option is set\.
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\fB\-\-[no\-]pass\-through\fR enable / disable passing through uncompressed files as\-is\. During decompression when pass\-through is enabled, unrecognized formats will be copied as\-is from the input to the output\. By default, pass\-through will occur when the output destination is stdout and the force (\fB\-f\fR) option is set\.
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.
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.IP "\(bu" 4
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\fB\-\-rm\fR: remove source file(s) after successful compression or decompression\. If used in combination with \-o, will trigger a confirmation prompt (which can be silenced with \-f), as this is a destructive operation\.
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\fB\-\-rm\fR: remove source file(s) after successful compression or decompression\. If used in combination with \fB\-o\fR, will trigger a confirmation prompt (which can be silenced with \fB\-f\fR), as this is a destructive operation\.
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.
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.IP "\(bu" 4
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\fB\-k\fR, \fB\-\-keep\fR: keep source file(s) after successful compression or decompression\. This is the default behavior\.
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@ -201,7 +222,7 @@ If input directory contains "\.\.", the files in this directory will be ignored\
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\fB\-h\fR/\fB\-H\fR, \fB\-\-help\fR: display help/long help and exit
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.
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.IP "\(bu" 4
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\fB\-V\fR, \fB\-\-version\fR: display version number and exit\. Advanced : \fB\-vV\fR also displays supported formats\. \fB\-vvV\fR also displays POSIX support\. \fB\-q\fR will only display the version number, suitable for machine reading\.
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\fB\-V\fR, \fB\-\-version\fR: display version number and exit\. Advanced: \fB\-vV\fR also displays supported formats\. \fB\-vvV\fR also displays POSIX support\. \fB\-q\fR will only display the version number, suitable for machine reading\.
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.
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.IP "\(bu" 4
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\fB\-v\fR, \fB\-\-verbose\fR: verbose mode, display more information
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@ -213,14 +234,14 @@ If input directory contains "\.\.", the files in this directory will be ignored\
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\fB\-\-no\-progress\fR: do not display the progress bar, but keep all other messages\.
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.
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.IP "\(bu" 4
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\fB\-\-show\-default\-cparams\fR: Shows the default compression parameters that will be used for a particular src file\. If the provided src file is not a regular file (e\.g\. named pipe), the cli will just output the default parameters\. That is, the parameters that are used when the src size is unknown\.
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\fB\-\-show\-default\-cparams\fR: shows the default compression parameters that will be used for a particular input file, based on the provided compression level and the input size\. If the provided file is not a regular file (e\.g\. a pipe), this flag will output the parameters used for inputs of unknown size\.
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.
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.IP "\(bu" 4
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\fB\-\-\fR: All arguments after \fB\-\-\fR are treated as files
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.
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.IP "" 0
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.
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.SS "gzip Operation modifiers"
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.SS "gzip Operation Modifiers"
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When invoked via a \fBgzip\fR symlink, \fBzstd\fR will support further options that intend to mimic the \fBgzip\fR behavior:
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.
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.TP
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@ -231,7 +252,7 @@ do not store the original filename and timestamps when compressing a file\. This
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\fB\-\-best\fR
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alias to the option \fB\-9\fR\.
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.
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.SS "Interactions with Environment Variables"
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.SS "Environment Variables"
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Employing environment variables to set parameters has security implications\. Therefore, this avenue is intentionally limited\. Only \fBZSTD_CLEVEL\fR and \fBZSTD_NBTHREADS\fR are currently supported\. They set the compression level and number of threads to use during compression, respectively\.
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.
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.P
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@ -251,7 +272,7 @@ They can both be overridden by corresponding command line arguments: \fB\-#\fR f
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Use FILEs as training set to create a dictionary\. The training set should ideally contain a lot of samples (> 100), and weight typically 100x the target dictionary size (for example, ~10 MB for a 100 KB dictionary)\. \fB\-\-train\fR can be combined with \fB\-r\fR to indicate a directory rather than listing all the files, which can be useful to circumvent shell expansion limits\.
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.
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.IP
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Since dictionary compression is mostly effective for small files, the expectation is that the training set will only contain small files\. In the case where some samples happen to be large, only the first 128 KB of these samples will be used for training\.
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Since dictionary compression is mostly effective for small files, the expectation is that the training set will only contain small files\. In the case where some samples happen to be large, only the first 128 KiB of these samples will be used for training\.
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.
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.IP
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\fB\-\-train\fR supports multithreading if \fBzstd\fR is compiled with threading support (default)\. Additional advanced parameters can be specified with \fB\-\-train\-fastcover\fR\. The legacy dictionary builder can be accessed with \fB\-\-train\-legacy\fR\. The slower cover dictionary builder can be accessed with \fB\-\-train\-cover\fR\. Default \fB\-\-train\fR is equivalent to \fB\-\-train\-fastcover=d=8,steps=4\fR\.
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@ -281,7 +302,10 @@ In situations where the training set is larger than maximum memory, the CLI will
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.
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.TP
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\fB\-\-dictID=#\fR
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A dictionary ID is a locally unique ID\. The decoder will use this value to verify it is using the right dictionary\. By default, zstd will create a 4\-bytes random number ID\. It\'s possible to provide an explicit number ID instead\. It\'s up to the dictionary manager to not assign twice the same ID to 2 different dictionaries\. Note that short numbers have an advantage : an ID < 256 will only need 1 byte in the compressed frame header, and an ID < 65536 will only need 2 bytes\. This compares favorably to 4 bytes default\.
|
||||
A dictionary ID is a locally unique ID\. The decoder will use this value to verify it is using the right dictionary\. By default, zstd will create a 4\-bytes random number ID\. It\'s possible to provide an explicit number ID instead\. It\'s up to the dictionary manager to not assign twice the same ID to 2 different dictionaries\. Note that short numbers have an advantage: an ID < 256 will only need 1 byte in the compressed frame header, and an ID < 65536 will only need 2 bytes\. This compares favorably to 4 bytes default\.
|
||||
.
|
||||
.IP
|
||||
Note that RFC8878 reserves IDs less than 32768 and greater than or equal to 2^31, so they should not be used in public\.
|
||||
.
|
||||
.TP
|
||||
\fB\-\-train\-cover[=k#,d=#,steps=#,split=#,shrink[=#]]\fR
|
||||
@ -366,7 +390,7 @@ cut file(s) into independent chunks of size # (default: no chunking)
|
||||
set process priority to real\-time
|
||||
.
|
||||
.P
|
||||
\fBOutput Format:\fR CompressionLevel#Filename : InputSize \-> OutputSize (CompressionRatio), CompressionSpeed, DecompressionSpeed
|
||||
\fBOutput Format:\fR CompressionLevel#Filename: InputSize \-> OutputSize (CompressionRatio), CompressionSpeed, DecompressionSpeed
|
||||
.
|
||||
.P
|
||||
\fBMethodology:\fR For both compression and decompression speed, the entire input is compressed/decompressed in\-memory to measure speed\. A run lasts at least 1 sec, so when files are small, they are compressed/decompressed several times per run, in order to improve measurement accuracy\.
|
||||
@ -377,14 +401,14 @@ set process priority to real\-time
|
||||
Specify the size of each compression job\. This parameter is only available when multi\-threading is enabled\. Each compression job is run in parallel, so this value indirectly impacts the nb of active threads\. Default job size varies depending on compression level (generally \fB4 * windowSize\fR)\. \fB\-B#\fR makes it possible to manually select a custom size\. Note that job size must respect a minimum value which is enforced transparently\. This minimum is either 512 KB, or \fBoverlapSize\fR, whichever is largest\. Different job sizes will lead to non\-identical compressed frames\.
|
||||
.
|
||||
.SS "\-\-zstd[=options]:"
|
||||
\fBzstd\fR provides 22 predefined compression levels\. The selected or default predefined compression level can be changed with advanced compression options\. The \fIoptions\fR are provided as a comma\-separated list\. You may specify only the options you want to change and the rest will be taken from the selected or default compression level\. The list of available \fIoptions\fR:
|
||||
\fBzstd\fR provides 22 predefined regular compression levels plus the fast levels\. This compression level is translated internally into a number of specific parameters that actually control the behavior of the compressor\. (You can see the result of this translation with \fB\-\-show\-default\-cparams\fR\.) These specific parameters can be overridden with advanced compression options\. The \fIoptions\fR are provided as a comma\-separated list\. You may specify only the options you want to change and the rest will be taken from the selected or default compression level\. The list of available \fIoptions\fR:
|
||||
.
|
||||
.TP
|
||||
\fBstrategy\fR=\fIstrat\fR, \fBstrat\fR=\fIstrat\fR
|
||||
Specify a strategy used by a match finder\.
|
||||
.
|
||||
.IP
|
||||
There are 9 strategies numbered from 1 to 9, from faster to stronger: 1=ZSTD_fast, 2=ZSTD_dfast, 3=ZSTD_greedy, 4=ZSTD_lazy, 5=ZSTD_lazy2, 6=ZSTD_btlazy2, 7=ZSTD_btopt, 8=ZSTD_btultra, 9=ZSTD_btultra2\.
|
||||
There are 9 strategies numbered from 1 to 9, from fastest to strongest: 1=\fBZSTD_fast\fR, 2=\fBZSTD_dfast\fR, 3=\fBZSTD_greedy\fR, 4=\fBZSTD_lazy\fR, 5=\fBZSTD_lazy2\fR, 6=\fBZSTD_btlazy2\fR, 7=\fBZSTD_btopt\fR, 8=\fBZSTD_btultra\fR, 9=\fBZSTD_btultra2\fR\.
|
||||
.
|
||||
.TP
|
||||
\fBwindowLog\fR=\fIwlog\fR, \fBwlog\fR=\fIwlog\fR
|
||||
@ -404,17 +428,17 @@ Specify the maximum number of bits for a hash table\.
|
||||
Bigger hash tables cause fewer collisions which usually makes compression faster, but requires more memory during compression\.
|
||||
.
|
||||
.IP
|
||||
The minimum \fIhlog\fR is 6 (64 B) and the maximum is 30 (1 GiB)\.
|
||||
The minimum \fIhlog\fR is 6 (64 entries / 256 B) and the maximum is 30 (1B entries / 4 GiB)\.
|
||||
.
|
||||
.TP
|
||||
\fBchainLog\fR=\fIclog\fR, \fBclog\fR=\fIclog\fR
|
||||
Specify the maximum number of bits for a hash chain or a binary tree\.
|
||||
Specify the maximum number of bits for the secondary search structure, whose form depends on the selected \fBstrategy\fR\.
|
||||
.
|
||||
.IP
|
||||
Higher numbers of bits increases the chance to find a match which usually improves compression ratio\. It also slows down compression speed and increases memory requirements for compression\. This option is ignored for the ZSTD_fast strategy\.
|
||||
Higher numbers of bits increases the chance to find a match which usually improves compression ratio\. It also slows down compression speed and increases memory requirements for compression\. This option is ignored for the \fBZSTD_fast\fR \fBstrategy\fR, which only has the primary hash table\.
|
||||
.
|
||||
.IP
|
||||
The minimum \fIclog\fR is 6 (64 B) and the maximum is 29 (524 Mib) on 32\-bit platforms and 30 (1 Gib) on 64\-bit platforms\.
|
||||
The minimum \fIclog\fR is 6 (64 entries / 256 B) and the maximum is 29 (512M entries / 2 GiB) on 32\-bit platforms and 30 (1B entries / 4 GiB) on 64\-bit platforms\.
|
||||
.
|
||||
.TP
|
||||
\fBsearchLog\fR=\fIslog\fR, \fBslog\fR=\fIslog\fR
|
||||
@ -441,20 +465,23 @@ The minimum \fImml\fR is 3 and the maximum is 7\.
|
||||
The impact of this field vary depending on selected strategy\.
|
||||
.
|
||||
.IP
|
||||
For ZSTD_btopt, ZSTD_btultra and ZSTD_btultra2, it specifies the minimum match length that causes match finder to stop searching\. A larger \fBtargetLength\fR usually improves compression ratio but decreases compression speed\. t For ZSTD_fast, it triggers ultra\-fast mode when > 0\. The value represents the amount of data skipped between match sampling\. Impact is reversed : a larger \fBtargetLength\fR increases compression speed but decreases compression ratio\.
|
||||
For \fBZSTD_btopt\fR, \fBZSTD_btultra\fR and \fBZSTD_btultra2\fR, it specifies the minimum match length that causes match finder to stop searching\. A larger \fBtargetLength\fR usually improves compression ratio but decreases compression speed\.
|
||||
.
|
||||
.IP
|
||||
For \fBZSTD_fast\fR, it triggers ultra\-fast mode when > 0\. The value represents the amount of data skipped between match sampling\. Impact is reversed: a larger \fBtargetLength\fR increases compression speed but decreases compression ratio\.
|
||||
.
|
||||
.IP
|
||||
For all other strategies, this field has no impact\.
|
||||
.
|
||||
.IP
|
||||
The minimum \fItlen\fR is 0 and the maximum is 128 Kib\.
|
||||
The minimum \fItlen\fR is 0 and the maximum is 128 KiB\.
|
||||
.
|
||||
.TP
|
||||
\fBoverlapLog\fR=\fIovlog\fR, \fBovlog\fR=\fIovlog\fR
|
||||
Determine \fBoverlapSize\fR, amount of data reloaded from previous job\. This parameter is only available when multithreading is enabled\. Reloading more data improves compression ratio, but decreases speed\.
|
||||
.
|
||||
.IP
|
||||
The minimum \fIovlog\fR is 0, and the maximum is 9\. 1 means "no overlap", hence completely independent jobs\. 9 means "full overlap", meaning up to \fBwindowSize\fR is reloaded from previous job\. Reducing \fIovlog\fR by 1 reduces the reloaded amount by a factor 2\. For example, 8 means "windowSize/2", and 6 means "windowSize/8"\. Value 0 is special and means "default" : \fIovlog\fR is automatically determined by \fBzstd\fR\. In which case, \fIovlog\fR will range from 6 to 9, depending on selected \fIstrat\fR\.
|
||||
The minimum \fIovlog\fR is 0, and the maximum is 9\. 1 means "no overlap", hence completely independent jobs\. 9 means "full overlap", meaning up to \fBwindowSize\fR is reloaded from previous job\. Reducing \fIovlog\fR by 1 reduces the reloaded amount by a factor 2\. For example, 8 means "windowSize/2", and 6 means "windowSize/8"\. Value 0 is special and means "default": \fIovlog\fR is automatically determined by \fBzstd\fR\. In which case, \fIovlog\fR will range from 6 to 9, depending on selected \fIstrat\fR\.
|
||||
.
|
||||
.TP
|
||||
\fBldmHashLog\fR=\fIlhlog\fR, \fBlhlog\fR=\fIlhlog\fR
|
||||
@ -514,6 +541,12 @@ The following parameters sets advanced compression options to something similar
|
||||
.P
|
||||
\fB\-\-zstd\fR=wlog=23,clog=23,hlog=22,slog=6,mml=3,tlen=48,strat=6
|
||||
.
|
||||
.SH "SEE ALSO"
|
||||
\fBzstdgrep\fR(1), \fBzstdless\fR(1), \fBgzip\fR(1), \fBxz\fR(1)
|
||||
.
|
||||
.P
|
||||
The \fIzstandard\fR format is specified in Y\. Collet, "Zstandard Compression and the \'application/zstd\' Media Type", https://www\.ietf\.org/rfc/rfc8878\.txt, Internet RFC 8878 (February 2021)\.
|
||||
.
|
||||
.SH "BUGS"
|
||||
Report bugs at: https://github\.com/facebook/zstd/issues
|
||||
.
|
||||
|
||||
Loading…
Reference in New Issue
Block a user