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zstd.1: added advanced compression options
This commit is contained in:
Przemyslaw Skibinski
parent
c71e552b2e
commit
25314428c9
109
programs/zstd.1
109
programs/zstd.1
@ -264,6 +264,115 @@ and weight typically 100x the target dictionary size (for example, 10 MB for a 1
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cut file into independent blocks of size # (default: no block)
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cut file into independent blocks of size # (default: no block)
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.SH ADVANCED COMPRESSION OPTIONS
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.TP
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.B \--zstd[=\fIoptions\fR]
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.PD
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\fBzstd\fR provides 22 predefined compression levels. The selected or default predefined compression level can be changed with advanced compression options.
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The \fIoptions\fR are provided as a comma-separated list. You may specify only the \fIoptions\fR you want to change and the rest will be taken from the selected or default compression level.
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The list of available \fIoptions\fR:
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.RS
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.TP
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.BI strategy= strat
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.PD 0
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.TP
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.BI strat= strat
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.PD
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Specify a strategy used by a match finder.
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.IP ""
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There are 8 strategies numbered from 0 to 7, from faster to stronger:
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0=ZSTD_fast, 1=ZSTD_dfast, 2=ZSTD_greedy, 3=ZSTD_lazy, 4=ZSTD_lazy2, 5=ZSTD_btlazy2, 6=ZSTD_btopt, 7=ZSTD_btopt2.
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.IP ""
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.TP
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.BI windowLog= wlog
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.PD 0
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.TP
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.BI wlog= wlog
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.PD
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Specify the maximum number of bits for a match distance.
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.IP ""
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The higher number of bits increases the chance to find a match what usually improves compression ratio.
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It also increases memory requirements for compressor and decompressor.
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.IP ""
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The minimum \fIwlog\fR is 10 (1 KiB) and the maximum is 25 (32 MiB) for 32-bit compilation and 27 (128 MiB) for 64-bit compilation.
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.IP ""
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.TP
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.BI hashLog= hlog
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.PD 0
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.TP
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.BI hlog= hlog
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.PD
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Specify the maximum number of bits for a hash table.
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.IP ""
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The bigger hash table causes less collisions what usually make compression faster but requires more memory during compression.
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.IP ""
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The minimum \fIhlog\fR is 6 (64 B) and the maximum is 25 (32 MiB) for 32-bit compilation and 27 (128 MiB) for 64-bit compilation.
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.TP
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.BI chainLog= clog
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.PD 0
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.TP
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.BI clog= clog
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.PD
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Specify the maximum number of bits for a hash chain or a binary tree.
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.IP ""
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The higher number of bits increases the chance to find a match what usually improves compression ratio.
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It also slows down compression speed and increases memory requirements for compression.
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This option is ignored for the ZSTD_fast strategy.
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.IP ""
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The minimum \fIclog\fR is 6 (64 B) and the maximum is 26 (64 MiB) for 32-bit compilation and 28 (256 MiB) for 64-bit compilation.
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.IP ""
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.TP
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.BI searchLog= slog
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.PD 0
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.TP
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.BI slog= slog
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.PD
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Specify the maximum number of searches in a hash chain or a binary tree using logarithmic scale.
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.IP ""
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The bigger number of searches increases the chance to find a match what usually improves compression ratio but decreases compression speed.
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.IP ""
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The minimum \fIslog\fR is 1 and the maximum is 24 for 32-bit compilation and 26 for 64-bit compilation.
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.IP ""
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.TP
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.BI searchLength= slen
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.PD 0
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.TP
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.BI slen= slen
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.PD
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Specify the minimum searched length of a match in a hash table.
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.IP ""
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The bigger search length usually decreases compression ratio but improves decompression speed.
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.IP ""
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The minimum \fIslen\fR is 3 and the maximum is 7.
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.IP ""
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.TP
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.BI targetLength= tlen
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.PD 0
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.TP
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.BI tlen= tlen
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.PD
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Specify the minimum match length that causes a match finder to interrupt searching of better matches.
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.IP ""
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The bigger minimum match length usually improves compression ratio but decreases compression speed.
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This option is used only with ZSTD_btopt and ZSTD_btopt2 strategies.
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.IP ""
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The minimum \fItlen\fR is 4 and the maximum is 999.
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.IP ""
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.PP
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.B An example
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.br
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The following parameters sets advanced compression options to predefined level 19 for files bigger than 256 KB:
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.IP ""
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\fB--zstd=\fRwindowLog=23,chainLog=23,hashLog=22,searchLog=6,searchLength=3,targetLength=48,strategy=6
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.SH BUGS
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.SH BUGS
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Report bugs at:- https://github.com/facebook/zstd/issues
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Report bugs at:- https://github.com/facebook/zstd/issues
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