Yann Collet
GitHub
commit
93ff2fb329
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@ -10,7 +10,7 @@ There are however other Makefile targets that create different variations of CLI
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- `zstd-decompress` : version of CLI which can only decompress zstd format
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#### Compilation variables
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### Compilation variables
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`zstd` scope can be altered by modifying the following `make` variables :
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- __HAVE_THREAD__ : multithreading is automatically enabled when `pthread` is detected.
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@ -61,6 +61,24 @@ There are however other Makefile targets that create different variations of CLI
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In which case, linking stage will fail if `lz4` library cannot be found.
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This is useful to prevent silent feature disabling.
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- __ZSTD_NOBENCH__ : `zstd` cli will be compiled without its integrated benchmark module.
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This can be useful to produce smaller binaries.
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In this case, the corresponding unit can also be excluded from compilation target.
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- __ZSTD_NODICT__ : `zstd` cli will be compiled without support for the integrated dictionary builder.
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This can be useful to produce smaller binaries.
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In this case, the corresponding unit can also be excluded from compilation target.
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- __ZSTD_NOCOMPRESS__ : `zstd` cli will be compiled without support for compression.
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The resulting binary will only be able to decompress files.
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This can be useful to produce smaller binaries.
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A corresponding `Makefile` target using this ability is `zstd-decompress`.
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- __ZSTD_NODECOMPRESS__ : `zstd` cli will be compiled without support for decompression.
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The resulting binary will only be able to compress files.
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This can be useful to produce smaller binaries.
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A corresponding `Makefile` target using this ability is `zstd-compress`.
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- __BACKTRACE__ : `zstd` can display a stack backtrace when execution
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generates a runtime exception. By default, this feature may be
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degraded/disabled on some platforms unless additional compiler directives are
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@ -69,11 +87,11 @@ There are however other Makefile targets that create different variations of CLI
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Example : `make zstd BACKTRACE=1`
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#### Aggregation of parameters
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### Aggregation of parameters
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CLI supports aggregation of parameters i.e. `-b1`, `-e18`, and `-i1` can be joined into `-b1e18i1`.
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#### Symlink shortcuts
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### Symlink shortcuts
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It's possible to invoke `zstd` through a symlink.
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When the name of the symlink has a specific value, it triggers an associated behavior.
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- `zstdmt` : compress using all cores available on local system.
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@ -86,7 +104,7 @@ When the name of the symlink has a specific value, it triggers an associated beh
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- `ungz`, `unxz` and `unlzma` will do the same, and will also remove source file by default (use `--keep` to preserve).
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#### Dictionary builder in Command Line Interface
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### Dictionary builder in Command Line Interface
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Zstd offers a training mode, which can be used to tune the algorithm for a selected
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type of data, by providing it with a few samples. The result of the training is stored
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in a file selected with the `-o` option (default name is `dictionary`),
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@ -106,7 +124,7 @@ Usage of the dictionary builder and created dictionaries with CLI:
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3. Decompress with the dictionary: `zstd --decompress FILE.zst -D dictionaryName`
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#### Benchmark in Command Line Interface
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### Benchmark in Command Line Interface
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CLI includes in-memory compression benchmark module for zstd.
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The benchmark is conducted using given filenames. The files are read into memory and joined together.
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It makes benchmark more precise as it eliminates I/O overhead.
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@ -118,7 +136,7 @@ One can select compression levels starting from `-b` and ending with `-e`.
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The `-i` parameter selects minimal time used for each of tested levels.
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#### Usage of Command Line Interface
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### Usage of Command Line Interface
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The full list of options can be obtained with `-h` or `-H` parameter:
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```
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Usage :
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@ -183,16 +201,19 @@ Benchmark arguments :
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--priority=rt : set process priority to real-time
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```
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#### Restricted usage of Environment Variables
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Using environment variables to set parameters has security implications.
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Therefore, this avenue is intentionally restricted.
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Only `ZSTD_CLEVEL` is supported currently, for setting compression level.
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`ZSTD_CLEVEL` can be used to set the level between 1 and 19 (the "normal" range).
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If the value of `ZSTD_CLEVEL` is not a valid integer, it will be ignored with a warning message.
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`ZSTD_CLEVEL` just replaces the default compression level (`3`).
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It can be overridden by corresponding command line arguments.
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### Passing parameters through Environment Variables
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`ZSTD_CLEVEL` can be used to modify the default compression level of `zstd`
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(usually set to `3`) to another value between 1 and 19 (the "normal" range).
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This can be useful when `zstd` CLI is invoked in a way that doesn't allow passing arguments.
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One such scenario is `tar --zstd`.
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As `ZSTD_CLEVEL` only replaces the default compression level,
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it can then be overridden by corresponding command line arguments.
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#### Long distance matching mode
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There is no "generic" way to pass "any kind of parameter" to `zstd` in a pass-through manner.
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Using environment variables for this purpose has security implications.
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Therefore, this avenue is intentionally restricted and only supports `ZSTD_CLEVEL`.
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### Long distance matching mode
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The long distance matching mode, enabled with `--long`, is designed to improve
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the compression ratio for files with long matches at a large distance (up to the
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maximum window size, `128 MiB`) while still maintaining compression speed.
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@ -216,12 +237,12 @@ Compression Speed vs Ratio | Decompression Speed
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| Method | Compression ratio | Compression speed | Decompression speed |
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|:-------|------------------:|-------------------------:|---------------------------:|
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| `zstd -1` | `5.065` | `284.8 MB/s` | `759.3 MB/s` |
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| `zstd -1` | `5.065` | `284.8 MB/s` | `759.3 MB/s` |
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| `zstd -5` | `5.826` | `124.9 MB/s` | `674.0 MB/s` |
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| `zstd -10` | `6.504` | `29.5 MB/s` | `771.3 MB/s` |
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| `zstd -1 --long` | `17.426` | `220.6 MB/s` | `1638.4 MB/s` |
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| `zstd -5 --long` | `19.661` | `165.5 MB/s` | `1530.6 MB/s`|
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| `zstd -10 --long`| `21.949` | `75.6 MB/s` | `1632.6 MB/s`|
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| `zstd -5 --long` | `19.661` | `165.5 MB/s` | `1530.6 MB/s` |
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| `zstd -10 --long`| `21.949` | `75.6 MB/s` | `1632.6 MB/s` |
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On this file, the compression ratio improves significantly with minimal impact
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on compression speed, and the decompression speed doubles.
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@ -243,7 +264,8 @@ The below table illustrates this on the [Silesia compression corpus].
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| `zstd -10` | `3.523` | `16.4 MB/s` | `489.2 MB/s` |
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| `zstd -10 --long`| `3.566` | `16.2 MB/s` | `415.7 MB/s` |
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#### zstdgrep
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### zstdgrep
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`zstdgrep` is a utility which makes it possible to `grep` directly a `.zst` compressed file.
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It's used the same way as normal `grep`, for example :
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