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diff --git a/src/zstd/programs/README.md b/src/zstd/programs/README.md new file mode 100644 index 00000000..2da9a6db --- /dev/null +++ b/src/zstd/programs/README.md @@ -0,0 +1,209 @@ +Command Line Interface for Zstandard library +============================================ + +Command Line Interface (CLI) can be created using the `make` command without any additional parameters. +There are however other Makefile targets that create different variations of CLI: +- `zstd` : default CLI supporting gzip-like arguments; includes dictionary builder, benchmark, and support for decompression of legacy zstd formats +- `zstd_nolegacy` : Same as `zstd` but without support for legacy zstd formats +- `zstd-small` : CLI optimized for minimal size; no dictionary builder, no benchmark, and no support for legacy zstd formats +- `zstd-compress` : version of CLI which can only compress into zstd format +- `zstd-decompress` : version of CLI which can only decompress zstd format + + +#### Compilation variables +`zstd` scope can be altered by modifying the following compilation variables : + +- __HAVE_THREAD__ : multithreading is automatically enabled when `pthread` is detected. + It's possible to disable multithread support, by setting HAVE_THREAD=0 . + Example : make zstd HAVE_THREAD=0 + It's also possible to force compilation with multithread support, using HAVE_THREAD=1. + In which case, linking stage will fail if `pthread` library cannot be found. + This might be useful to prevent silent feature disabling. + +- __HAVE_ZLIB__ : `zstd` can compress and decompress files in `.gz` format. + This is ordered through command `--format=gzip`. + Alternatively, symlinks named `gzip` or `gunzip` will mimic intended behavior. + `.gz` support is automatically enabled when `zlib` library is detected at build time. + It's possible to disable `.gz` support, by setting HAVE_ZLIB=0. + Example : make zstd HAVE_ZLIB=0 + It's also possible to force compilation with zlib support, using HAVE_ZLIB=1. + In which case, linking stage will fail if `zlib` library cannot be found. + This might be useful to prevent silent feature disabling. + +- __HAVE_LZMA__ : `zstd` can compress and decompress files in `.xz` and `.lzma` formats. + This is ordered through commands `--format=xz` and `--format=lzma` respectively. + Alternatively, symlinks named `xz`, `unxz`, `lzma`, or `unlzma` will mimic intended behavior. + `.xz` and `.lzma` support is automatically enabled when `lzma` library is detected at build time. + It's possible to disable `.xz` and `.lzma` support, by setting HAVE_LZMA=0 . + Example : make zstd HAVE_LZMA=0 + It's also possible to force compilation with lzma support, using HAVE_LZMA=1. + In which case, linking stage will fail if `lzma` library cannot be found. + This might be useful to prevent silent feature disabling. + +- __HAVE_LZ4__ : `zstd` can compress and decompress files in `.lz4` formats. + This is ordered through commands `--format=lz4`. + Alternatively, symlinks named `lz4`, or `unlz4` will mimic intended behavior. + `.lz4` support is automatically enabled when `lz4` library is detected at build time. + It's possible to disable `.lz4` support, by setting HAVE_LZ4=0 . + Example : make zstd HAVE_LZ4=0 + It's also possible to force compilation with lz4 support, using HAVE_LZ4=1. + In which case, linking stage will fail if `lz4` library cannot be found. + This might be useful to prevent silent feature disabling. + +- __ZSTD_LEGACY_SUPPORT__ : `zstd` can decompress files compressed by older versions of `zstd`. + Starting v0.8.0, all versions of `zstd` produce frames compliant with the [specification](../doc/zstd_compression_format.md), and are therefore compatible. + But older versions (< v0.8.0) produced different, incompatible, frames. + By default, `zstd` supports decoding legacy formats >= v0.4.0 (`ZSTD_LEGACY_SUPPORT=4`). + This can be altered by modifying this compilation variable. + `ZSTD_LEGACY_SUPPORT=1` means "support all formats >= v0.1.0". + `ZSTD_LEGACY_SUPPORT=2` means "support all formats >= v0.2.0", and so on. + `ZSTD_LEGACY_SUPPORT=0` means _DO NOT_ support any legacy format. + if `ZSTD_LEGACY_SUPPORT >= 8`, it's the same as `0`, since there is no legacy format after `7`. + Note : `zstd` only supports decoding older formats, and cannot generate any legacy format. + + +#### Aggregation of parameters +CLI supports aggregation of parameters i.e. `-b1`, `-e18`, and `-i1` can be joined into `-b1e18i1`. + + +#### Dictionary builder in Command Line Interface +Zstd offers a training mode, which can be used to tune the algorithm for a selected +type of data, by providing it with a few samples. The result of the training is stored +in a file selected with the `-o` option (default name is `dictionary`), +which can be loaded before compression and decompression. + +Using a dictionary, the compression ratio achievable on small data improves dramatically. +These compression gains are achieved while simultaneously providing faster compression and decompression speeds. +Dictionary work if there is some correlation in a family of small data (there is no universal dictionary). +Hence, deploying one dictionary per type of data will provide the greater benefits. +Dictionary gains are mostly effective in the first few KB. Then, the compression algorithm +will rely more and more on previously decoded content to compress the rest of the file. + +Usage of the dictionary builder and created dictionaries with CLI: + +1. Create the dictionary : `zstd --train PathToTrainingSet/* -o dictionaryName` +2. Compress with the dictionary: `zstd FILE -D dictionaryName` +3. Decompress with the dictionary: `zstd --decompress FILE.zst -D dictionaryName` + + +#### Benchmark in Command Line Interface +CLI includes in-memory compression benchmark module for zstd. +The benchmark is conducted using given filenames. The files are read into memory and joined together. +It makes benchmark more precise as it eliminates I/O overhead. +Multiple filenames can be supplied, as multiple parameters, with wildcards, +or names of directories can be used as parameters with `-r` option. + +The benchmark measures ratio, compressed size, compression and decompression speed. +One can select compression levels starting from `-b` and ending with `-e`. +The `-i` parameter selects minimal time used for each of tested levels. + + +#### Usage of Command Line Interface +The full list of options can be obtained with `-h` or `-H` parameter: +``` +Usage : + zstd [args] [FILE(s)] [-o file] + +FILE : a filename + with no FILE, or when FILE is - , read standard input +Arguments : + -# : # compression level (1-19, default:3) + -d : decompression + -D file: use `file` as Dictionary + -o file: result stored into `file` (only if 1 input file) + -f : overwrite output without prompting and (de)compress links +--rm : remove source file(s) after successful de/compression + -k : preserve source file(s) (default) + -h/-H : display help/long help and exit + +Advanced arguments : + -V : display Version number and exit + -v : verbose mode; specify multiple times to increase verbosity + -q : suppress warnings; specify twice to suppress errors too + -c : force write to standard output, even if it is the console + -l : print information about zstd compressed files +--ultra : enable levels beyond 19, up to 22 (requires more memory) +--long : enable long distance matching (requires more memory) +--no-dictID : don't write dictID into header (dictionary compression) +--[no-]check : integrity check (default:enabled) + -r : operate recursively on directories +--format=gzip : compress files to the .gz format +--format=xz : compress files to the .xz format +--format=lzma : compress files to the .lzma format +--test : test compressed file integrity +--[no-]sparse : sparse mode (default:disabled) + -M# : Set a memory usage limit for decompression +-- : All arguments after "--" are treated as files + +Dictionary builder : +--train ## : create a dictionary from a training set of files +--train-cover[=k=#,d=#,steps=#] : use the cover algorithm with optional args +--train-legacy[=s=#] : use the legacy algorithm with selectivity (default: 9) + -o file : `file` is dictionary name (default: dictionary) +--maxdict=# : limit dictionary to specified size (default : 112640) +--dictID=# : force dictionary ID to specified value (default: random) + +Benchmark arguments : + -b# : benchmark file(s), using # compression level (default : 1) + -e# : test all compression levels from -bX to # (default: 1) + -i# : minimum evaluation time in seconds (default : 3s) + -B# : cut file into independent blocks of size # (default: no block) +--priority=rt : set process priority to real-time +``` + + +#### Long distance matching mode +The long distance matching mode, enabled with `--long`, is designed to improve +the compression ratio for files with long matches at a large distance (up to the +maximum window size, `128 MiB`) while still maintaining compression speed. + +Enabling this mode sets the window size to `128 MiB` and thus increases the memory +usage for both the compressor and decompressor. Performance in terms of speed is +dependent on long matches being found. Compression speed may degrade if few long +matches are found. Decompression speed usually improves when there are many long +distance matches. + +Below are graphs comparing the compression speed, compression ratio, and +decompression speed with and without long distance matching on an ideal use +case: a tar of four versions of clang (versions `3.4.1`, `3.4.2`, `3.5.0`, +`3.5.1`) with a total size of `244889600 B`. This is an ideal use case as there +are many long distance matches within the maximum window size of `128 MiB` (each +version is less than `128 MiB`). + +Compression Speed vs Ratio | Decompression Speed +---------------------------|--------------------- + |  + +| Method | Compression ratio | Compression speed | Decompression speed | +|:-------|------------------:|-------------------------:|---------------------------:| +| `zstd -1` | `5.065` | `284.8 MB/s` | `759.3 MB/s` | +| `zstd -5` | `5.826` | `124.9 MB/s` | `674.0 MB/s` | +| `zstd -10` | `6.504` | `29.5 MB/s` | `771.3 MB/s` | +| `zstd -1 --long` | `17.426` | `220.6 MB/s` | `1638.4 MB/s` | +| `zstd -5 --long` | `19.661` | `165.5 MB/s` | `1530.6 MB/s`| +| `zstd -10 --long`| `21.949` | `75.6 MB/s` | `1632.6 MB/s`| + +On this file, the compression ratio improves significantly with minimal impact +on compression speed, and the decompression speed doubles. + +On the other extreme, compressing a file with few long distance matches (such as +the [Silesia compression corpus]) will likely lead to a deterioration in +compression speed (for lower levels) with minimal change in compression ratio. + +The below table illustrates this on the [Silesia compression corpus]. + +[Silesia compression corpus]: http://sun.aei.polsl.pl/~sdeor/index.php?page=silesia + +| Method | Compression ratio | Compression speed | Decompression speed | +|:-------|------------------:|-------------------------:|---------------------------:| +| `zstd -1` | `2.878` | `231.7 MB/s` | `594.4 MB/s` | +| `zstd -1 --long` | `2.929` | `106.5 MB/s` | `517.9 MB/s` | +| `zstd -5` | `3.274` | `77.1 MB/s` | `464.2 MB/s` | +| `zstd -5 --long` | `3.319` | `51.7 MB/s` | `371.9 MB/s` | +| `zstd -10` | `3.523` | `16.4 MB/s` | `489.2 MB/s` | +| `zstd -10 --long`| `3.566` | `16.2 MB/s` | `415.7 MB/s` | + + + + + |