fix #1115
Yann Collet
parent
66b81817b5
commit
b824d213cb
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@ -1,5 +1,5 @@
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.TH "ZSTD" "1" "2018-01-27" "zstd 1.3.4" "User Commands"
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.TH "ZSTD" "1" "2018-05-12" "zstd 1.3.4" "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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@ -111,8 +111,16 @@ enables long distance matching with \fB#\fR \fBwindowLog\fR, if not \fB#\fR is n
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Note: If \fBwindowLog\fR is set to larger than 27, \fB\-\-long=windowLog\fR or \fB\-\-memory=windowSize\fR needs to be passed to the decompressor\.
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.TP
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\fB\-\-fast[=#]\fR
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switch to ultra\-fast compression levels\. If \fB=#\fR is not present, it defaults to \fB1\fR\. The higher the value, the faster the compression speed, at the cost of some compression ratio\. This setting overwrites compression level if one was set previously\. Similarly, if a compression level is set after \fB\-\-fast\fR, it overrides it\.
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.TP
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\fB\-T#\fR, \fB\-\-threads=#\fR
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Compress using \fB#\fR 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 ZSTDMT_NBTHREADS_MAX==256\. This modifier does nothing if \fBzstd\fR is compiled without multithread support\.
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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 ZSTDMT_NBTHREADS_MAX==200\. This modifier does nothing if \fBzstd\fR is compiled without multithread support\.
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.TP
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\fB\-\-single\-thread\fR
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Does not spawn a thread for compression, use caller thread instead\. This is the only available mode when multithread support is disabled\. In this mode, compression is serialized with I/O\. (This is different from \fB\-T1\fR, which spawns 1 compression thread in parallel of I/O)\. Single\-thread mode also features lower memory usage\.
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.TP
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\fB\-D file\fR
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@ -335,13 +343,19 @@ The minimum \fIslen\fR is 3 and the maximum is 7\.
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.TP
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\fBtargetLen\fR=\fItlen\fR, \fBtlen\fR=\fItlen\fR
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Specify the minimum match length that causes a match finder to stop searching for better matches\.
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The impact of this field vary depending on selected strategy\.
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.IP
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A larger minimum match length usually improves compression ratio but decreases compression speed\. This option is only used with strategies ZSTD_btopt and ZSTD_btultra\.
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For ZSTD_btopt and ZSTD_btultra, it specifies the minimum match length that causes match finder to stop searching for better matches\. A larger \fBtargetLen\fR usually improves compression ratio but decreases compression speed\.
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.IP
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The minimum \fItlen\fR is 4 and the maximum is 999\.
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For ZSTD_fast, it specifies the amount of data skipped between match sampling\. Impact is reversed : a larger \fBtargetLen\fR increases compression speed but decreases compression ratio\.
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.IP
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For all other strategies, this field has no impact\.
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.IP
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The minimum \fItlen\fR is 1 and the maximum is 999\.
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.TP
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\fBoverlapLog\fR=\fIovlog\fR, \fBovlog\fR=\fIovlog\fR
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@ -374,7 +388,7 @@ This option is ignored unless long distance matching is enabled\.
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Larger/very small values usually decrease compression ratio\.
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.IP
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The minumum \fIldmslen\fR is 4 and the maximum is 4096 (default: 64)\.
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The minimum \fIldmslen\fR is 4 and the maximum is 4096 (default: 64)\.
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.TP
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\fBldmBucketSizeLog\fR=\fIldmblog\fR, \fBldmblog\fR=\fIldmblog\fR
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@ -402,14 +416,14 @@ Larger values will improve compression speed\. Deviating far from the default va
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.IP
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The default value is \fBwlog \- ldmhlog\fR\.
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.SS "\-B#:"
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Select the size of each compression job\. This parameter is available only when multi\-threading is enabled\. Default value is \fB4 * windowSize\fR, which means it varies depending on compression level\. \fB\-B#\fR makes it possible to select a custom value\. Note that job size must respect a minimum value which is enforced transparently\. This minimum is either 1 MB, or \fBoverlapSize\fR, whichever is largest\.
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.SS "Example"
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The following parameters sets advanced compression options to those of predefined level 19 for files bigger than 256 KB:
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The following parameters sets advanced compression options to something similar to predefined level 19 for files bigger than 256 KB:
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.P
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\fB\-\-zstd\fR=windowLog=23,chainLog=23,hashLog=22,searchLog=6,searchLength=3,targetLength=48,strategy=6
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\fB\-\-zstd\fR=wlog=23,clog=23,hlog=22,slog=6,slen=3,tlen=48,strat=6
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.SS "\-B#:"
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Select the size of each compression job\. This parameter is available only when multi\-threading is enabled\. Default value is \fB4 * windowSize\fR, which means it varies depending on compression level\. \fB\-B#\fR makes it possible to select a custom value\. Note that job size must respect a minimum value which is enforced transparently\. This minimum is either 1 MB, or \fBoverlapSize\fR, whichever is largest\.
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.SH "BUGS"
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Report bugs at: https://github\.com/facebook/zstd/issues
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@ -392,7 +392,7 @@ The list of available _options_:
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Larger/very small values usually decrease compression ratio.
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The minumum _ldmslen_ is 4 and the maximum is 4096 (default: 64).
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The minimum _ldmslen_ is 4 and the maximum is 4096 (default: 64).
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- `ldmBucketSizeLog`=_ldmblog_, `ldmblog`=_ldmblog_:
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Specify the size of each bucket for the hash table used for long distance
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@ -416,6 +416,12 @@ The list of available _options_:
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The default value is `wlog - ldmhlog`.
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### Example
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The following parameters sets advanced compression options to something
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similar to predefined level 19 for files bigger than 256 KB:
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`--zstd`=wlog=23,clog=23,hlog=22,slog=6,slen=3,tlen=48,strat=6
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### -B#:
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Select the size of each compression job.
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This parameter is available only when multi-threading is enabled.
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@ -424,12 +430,6 @@ Default value is `4 * windowSize`, which means it varies depending on compressio
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Note that job size must respect a minimum value which is enforced transparently.
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This minimum is either 1 MB, or `overlapSize`, whichever is largest.
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### Example
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The following parameters sets advanced compression options to those of
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predefined level 19 for files bigger than 256 KB:
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`--zstd`=windowLog=23,chainLog=23,hashLog=22,searchLog=6,searchLength=3,targetLength=48,strategy=6
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BUGS
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----
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Report bugs at: https://github.com/facebook/zstd/issues
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