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updated documentation on multithreading modes

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Yann Collet
2017-04-01 00:36:31 -07:00
parent 30c7698970
commit 805c5a3efb
3 changed files with 53 additions and 13 deletions
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programs/zstd.1
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@@ -1,5 +1,5 @@
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.TH "ZSTD" "1" "March 2017" "zstd 1.1.5" "User Commands"
.TH "ZSTD" "1" "April 2017" "zstd 1.1.5" "User Commands"
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.SH "NAME"
\fBzstd\fR \- zstd, unzstd, zstdcat \- Compress or decompress \.zst files
@@ -97,6 +97,10 @@ Use FILEs as a training set to create a dictionary\. The training set should con
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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.TP
\fB\-T#\fR
Compress using # threads (default: 1)\. This modifier is only available if \fBzstd\fR was compiled with multithreading support\.
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.TP
\fB\-D file\fR
use \fBfile\fR as Dictionary to compress or decompress FILE(s)
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@@ -126,7 +130,7 @@ remove source file(s) after successful compression or decompression
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.TP
\fB\-k\fR, \fB\-\-keep\fR
keep source file(s) after successful compression or decompression\. This is the default behaviour\.
keep source file(s) after successful compression or decompression\. This is the default behavior\.
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.TP
\fB\-r\fR
@@ -150,7 +154,7 @@ suppress warnings, interactivity, and notifications\. specify twice to suppress
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.TP
\fB\-C\fR, \fB\-\-[no\-]check\fR
add integrety check computed from uncompressed data (default : enabled)
add integrity check computed from uncompressed data (default : enabled)
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.TP
\fB\-\-\fR
@@ -226,6 +230,9 @@ set process priority to real\-time
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.SH "ADVANCED COMPRESSION OPTIONS"
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.SS "\-B#:"
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 "\-\-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:
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@@ -293,6 +300,13 @@ A larger minimum match length usually improves compression ratio but decreases c
.IP
The minimum \fItlen\fR is 4 and the maximum is 999\.
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.TP
\fBoverlapLog\fR=\fIovlog\fR, \fBovlog\fR=\fIovlog\fR
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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.IP
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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.SS "Example"
The following parameters sets advanced compression options to those of predefined level 19 for files bigger than 256 KB:
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