57 lines
2.9 KiB
Markdown
57 lines
2.9 KiB
Markdown
# Parallel Zstandard (PZstandard)
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Parallel Zstandard is a Pigz-like tool for Zstandard.
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It provides Zstandard format compatible compression and decompression that is able to utilize multiple cores.
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It breaks the input up into equal sized chunks and compresses each chunk independently into a Zstandard frame.
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It then concatenates the frames together to produce the final compressed output.
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Pzstandard will write a 12 byte header for each frame that is a skippable frame in the Zstandard format, which tells PZstandard the size of the next compressed frame.
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PZstandard supports parallel decompression of files compressed with PZstandard.
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When decompressing files compressed with Zstandard, PZstandard does IO in one thread, and decompression in another.
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## Usage
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PZstandard supports the same command line interface as Zstandard, but also provides the `-p` option to specify the number of threads.
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Dictionary mode is not currently supported.
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Basic usage
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pzstd input-file -o output-file -p num-threads -# # Compression
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pzstd -d input-file -o output-file -p num-threads # Decompression
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PZstandard also supports piping and fifo pipes
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cat input-file | pzstd -p num-threads -# -c > /dev/null
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For more options
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pzstd --help
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PZstandard tries to pick a smart default number of threads if not specified (displayed in `pzstd --help`).
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If this number is not suitable, during compilation you can define `PZSTD_NUM_THREADS` to the number of threads you prefer.
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## Benchmarks
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As a reference, PZstandard and Pigz were compared on an Intel Core i7 @ 3.1 GHz, each using 4 threads, with the [Silesia compression corpus](http://sun.aei.polsl.pl/~sdeor/index.php?page=silesia).
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Compression Speed vs Ratio with 4 Threads | Decompression Speed with 4 Threads
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------------------------------------------|-----------------------------------
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The test procedure was to run each of the following commands 2 times for each compression level, and take the minimum time.
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time pzstd -# -p 4 -c silesia.tar > silesia.tar.zst
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time pzstd -d -p 4 -c silesia.tar.zst > /dev/null
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time pigz -# -p 4 -k -c silesia.tar > silesia.tar.gz
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time pigz -d -p 4 -k -c silesia.tar.gz > /dev/null
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PZstandard was tested using compression levels 1-19, and Pigz was tested using compression levels 1-9.
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Pigz cannot do parallel decompression, it simply does each of reading, decompression, and writing on separate threads.
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## Tests
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Tests require that you have [gtest](https://github.com/google/googletest) installed.
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Set `GTEST_INC` and `GTEST_LIB` in `Makefile` to specify the location of the gtest headers and libraries.
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Alternatively, run `make googletest`, which will clone googletest and build it.
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Run `make tests && make check` to run tests.
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