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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.md
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@@ -99,6 +99,9 @@ the last one takes effect.
* `--ultra`:
unlocks high compression levels 20+ (maximum 22), using a lot more memory.
Note that decompression will also require more memory when using these levels.
* `-T#`:
Compress using # threads (default: 1).
This modifier is only available if `zstd` was compiled with multithreading support.
* `-D file`:
use `file` as Dictionary to compress or decompress FILE(s)
* `--nodictID`:
@@ -123,7 +126,7 @@ the last one takes effect.
remove source file(s) after successful compression or decompression
* `-k`, `--keep`:
keep source file(s) after successful compression or decompression.
This is the default behaviour.
This is the default behavior.
* `-r`:
operate recursively on dictionaries
* `-h`/`-H`, `--help`:
@@ -136,10 +139,11 @@ the last one takes effect.
suppress warnings, interactivity, and notifications.
specify twice to suppress errors too.
* `-C`, `--[no-]check`:
add integrety check computed from uncompressed data (default : enabled)
add integrity check computed from uncompressed data (default : enabled)
* `--`:
All arguments after `--` are treated as files
DICTIONARY BUILDER
------------------
`zstd` offers _dictionary_ compression,
@@ -218,8 +222,17 @@ BENCHMARK
* `--priority=rt`:
set process priority to real-time
ADVANCED COMPRESSION OPTIONS
----------------------------
### -B#:
Select the size of each compression job.
This parameter is available only when multi-threading is enabled.
Default value is `4 * windowSize`, which means it varies depending on compression level.
`-B#` 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 `overlapSize`, whichever is largest.
### --zstd[=options]:
`zstd` provides 22 predefined compression levels.
The selected or default predefined compression level can be changed with
@@ -290,6 +303,19 @@ The list of available _options_:
The minimum _tlen_ is 4 and the maximum is 999.
- `overlapLog`=_ovlog_, `ovlog`=_ovlog_:
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.
The minimum _ovlog_ is 0, and the maximum is 9.
0 means "no overlap", hence completely independent jobs.
9 means "full overlap", meaning up to `windowSize` is reloaded from previous job.
Reducing _ovlog_ by 1 reduces the amount of reload by a factor 2.
Default _ovlog_ is 6, which means "reload `windowSize / 8`".
Exception : the maximum compression level (22) has a default _ovlog_ of 9.
### Example
The following parameters sets advanced compression options to those of
predefined level 19 for files bigger than 256 KB: