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updated documentation on multithreading modes
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Yann Collet
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.TH "ZSTD" "1" "March 2017" "zstd 1.1.5" "User Commands"
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.TH "ZSTD" "1" "April 2017" "zstd 1.1.5" "User Commands"
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.
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.SH "NAME"
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\fBzstd\fR \- zstd, unzstd, zstdcat \- Compress or decompress \.zst files
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@ -97,6 +97,10 @@ Use FILEs as a training set to create a dictionary\. The training set should con
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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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.
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.TP
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\fB\-T#\fR
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Compress using # threads (default: 1)\. This modifier is only available if \fBzstd\fR was compiled with multithreading support\.
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.
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.TP
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\fB\-D file\fR
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use \fBfile\fR as Dictionary to compress or decompress FILE(s)
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.
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@ -126,7 +130,7 @@ remove source file(s) after successful compression or decompression
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.
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.TP
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\fB\-k\fR, \fB\-\-keep\fR
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keep source file(s) after successful compression or decompression\. This is the default behaviour\.
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keep source file(s) after successful compression or decompression\. This is the default behavior\.
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.
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.TP
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\fB\-r\fR
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@ -150,7 +154,7 @@ suppress warnings, interactivity, and notifications\. specify twice to suppress
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.
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.TP
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\fB\-C\fR, \fB\-\-[no\-]check\fR
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add integrety check computed from uncompressed data (default : enabled)
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add integrity check computed from uncompressed data (default : enabled)
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.
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.TP
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\fB\-\-\fR
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@ -226,6 +230,9 @@ set process priority to real\-time
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.
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.SH "ADVANCED COMPRESSION OPTIONS"
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.
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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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.
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.SS "\-\-zstd[=options]:"
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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\. 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:
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.
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@ -293,6 +300,13 @@ A larger minimum match length usually improves compression ratio but decreases c
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.IP
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The minimum \fItlen\fR is 4 and the maximum is 999\.
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.
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.TP
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\fBoverlapLog\fR=\fIovlog\fR, \fBovlog\fR=\fIovlog\fR
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Select the amount of data reloaded from previous job into next one\. Reloading more data improves compression ratio, but decreases speed\. This parameter is only available if multithreading is enabled\.
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.
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.IP
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The minimum \fIovlog\fR is 0, and the maximum is 9\. 0 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 amount of reload by a factor 2\. Default \fIovlog\fR is 6, which means "reload \fBwindowSize / 8\fR"\. Exception : the maximum compression level (22) has a default \fIovlog\fR of 9\.
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.
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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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.
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@ -99,6 +99,9 @@ the last one takes effect.
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* `--ultra`:
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unlocks high compression levels 20+ (maximum 22), using a lot more memory.
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Note that decompression will also require more memory when using these levels.
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* `-T#`:
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Compress using # threads (default: 1).
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This modifier is only available if `zstd` was compiled with multithreading support.
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* `-D file`:
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use `file` as Dictionary to compress or decompress FILE(s)
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* `--nodictID`:
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@ -123,7 +126,7 @@ the last one takes effect.
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remove source file(s) after successful compression or decompression
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* `-k`, `--keep`:
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keep source file(s) after successful compression or decompression.
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This is the default behaviour.
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This is the default behavior.
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* `-r`:
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operate recursively on dictionaries
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* `-h`/`-H`, `--help`:
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@ -136,10 +139,11 @@ the last one takes effect.
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suppress warnings, interactivity, and notifications.
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specify twice to suppress errors too.
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* `-C`, `--[no-]check`:
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add integrety check computed from uncompressed data (default : enabled)
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add integrity check computed from uncompressed data (default : enabled)
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* `--`:
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All arguments after `--` are treated as files
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DICTIONARY BUILDER
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------------------
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`zstd` offers _dictionary_ compression,
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@ -218,8 +222,17 @@ BENCHMARK
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* `--priority=rt`:
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set process priority to real-time
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ADVANCED COMPRESSION OPTIONS
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----------------------------
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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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Default value is `4 * windowSize`, which means it varies depending on compression level.
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`-B#` makes it possible to select a custom value.
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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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### --zstd[=options]:
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`zstd` provides 22 predefined compression levels.
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The selected or default predefined compression level can be changed with
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@ -290,6 +303,19 @@ The list of available _options_:
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The minimum _tlen_ is 4 and the maximum is 999.
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- `overlapLog`=_ovlog_, `ovlog`=_ovlog_:
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Select the amount of data reloaded from previous job into next one.
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Reloading more data improves compression ratio, but decreases speed.
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This parameter is only available if multithreading is enabled.
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The minimum _ovlog_ is 0, and the maximum is 9.
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0 means "no overlap", hence completely independent jobs.
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9 means "full overlap", meaning up to `windowSize` is reloaded from previous job.
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Reducing _ovlog_ by 1 reduces the amount of reload by a factor 2.
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Default _ovlog_ is 6, which means "reload `windowSize / 8`".
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Exception : the maximum compression level (22) has a default _ovlog_ of 9.
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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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@ -113,19 +113,20 @@ static int usage_advanced(const char* programName)
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DISPLAY( "\n");
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DISPLAY( "Advanced arguments :\n");
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DISPLAY( " -V : display Version number and exit\n");
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DISPLAY( " -v : verbose mode; specify multiple times to increase log level (default:%d)\n", DEFAULT_DISPLAY_LEVEL);
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DISPLAY( " -v : verbose mode; specify multiple times to increase verbosity\n");
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DISPLAY( " -q : suppress warnings; specify twice to suppress errors too\n");
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DISPLAY( " -c : force write to standard output, even if it is the console\n");
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#ifdef UTIL_HAS_CREATEFILELIST
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DISPLAY( " -r : operate recursively on directories \n");
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#endif
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#ifndef ZSTD_NOCOMPRESS
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DISPLAY( "--ultra : enable levels beyond %i, up to %i (requires more memory)\n", ZSTDCLI_CLEVEL_MAX, ZSTD_maxCLevel());
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DISPLAY( "--no-dictID : don't write dictID into header (dictionary compression)\n");
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DISPLAY( "--[no-]check : integrity check (default:enabled) \n");
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#ifdef ZSTD_MULTITHREAD
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DISPLAY( " -T# : use # threads for compression (default:1) \n");
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DISPLAY( " -B# : select size of independent sections (default:0==automatic) \n");
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DISPLAY( " -B# : select size of each job (default:0==automatic) \n");
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#endif
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DISPLAY( "--no-dictID : don't write dictID into header (dictionary compression)\n");
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DISPLAY( "--[no-]check : integrity check (default:enabled) \n");
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#endif
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#ifdef UTIL_HAS_CREATEFILELIST
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DISPLAY( " -r : operate recursively on directories \n");
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#endif
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#ifdef ZSTD_GZCOMPRESS
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DISPLAY( "--format=gzip : compress files to the .gz format \n");
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@ -134,7 +135,6 @@ static int usage_advanced(const char* programName)
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DISPLAY( "--format=xz : compress files to the .xz format \n");
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DISPLAY( "--format=lzma : compress files to the .lzma format \n");
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#endif
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#endif
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#ifndef ZSTD_NODECOMPRESS
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DISPLAY( "--test : test compressed file integrity \n");
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#if ZSTD_SPARSE_DEFAULT
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