82 lines
3.8 KiB
Markdown
82 lines
3.8 KiB
Markdown
Pcompress
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=========
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Copyright (C) 2012 Moinak Ghosh. All rights reserved.
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Use is subject to license terms.
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Pcompress is a utility to do compression and decompression in parallel by
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splitting input data into chunks. It has a modular structure and includes
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support for multiple algorithms like LZMA, Bzip2, PPMD, etc., with CRC64
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chunk checksums. SSE optimizations for the bundled LZMA are included. It
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also implements chunk-level Content-Aware Deduplication and Delta
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Compression features based on a Semi-Rabin Fingerprinting scheme. Delta
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Compression is implemented via the widely popular bsdiff algorithm.
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Similarity is detected using a custom hashing of maximal features of a
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block. When doing chunk-level dedupe it attempts to merge adjacent
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non-duplicate blocks index entries into a single larger entry to reduce
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metadata. In addition to all these it can internally split chunks at
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rabin boundaries to help dedupe and compression.
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It has low metadata overhead and overlaps I/O and compression to achieve
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maximum parallelism. It also bundles a simple slab allocator to speed
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repeated allocation of similar chunks. It can work in pipe mode, reading
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from stdin and writing to stdout. It also provides some adaptive compression
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modes in which multiple algorithms are tried per chunk to determine the best
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one for the given chunk. Finally it support 14 compression levels to allow
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for ultra compression modes in some algorithms.
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Usage
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=====
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To compress a file:
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pcompress -c <algorithm> [-l <compress level>] [-s <chunk size>] <file>
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Where <algorithm> can be the folowing:
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lzfx - Very fast and small algorithm based on LZF.
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lz4 - Ultra fast, high-throughput algorithm reaching RAM B/W at level1.
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zlib - The base Zlib format compression (not Gzip).
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lzma - The LZMA (Lempel-Ziv Markov) algorithm from 7Zip.
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bzip2 - Bzip2 Algorithm from libbzip2.
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ppmd - The PPMd algorithm excellent for textual data. PPMd requires
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at least 64MB X CPUs more memory than the other modes.
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adapt - Adaptive mode where ppmd or bzip2 will be used per chunk,
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depending on which one produces better compression. This mode
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is obviously fairly slow and requires lots of memory.
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adapt2 - Adaptive mode which includes ppmd and lzma. This requires
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more memory than adapt mode, is slower and potentially gives
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the best compression.
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<chunk_size> - This can be in bytes or can use the following suffixes:
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g - Gigabyte, m - Megabyte, k - Kilobyte.
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Larger chunks produce better compression at the cost of memory.
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<compress_level> - Can be a number from 0 meaning minimum and 14 meaning
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maximum compression.
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To decompress a file compressed using above command:
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pcompress -d <compressed file> <target file>
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To operate as a pipe, read from stdin and write to stdout:
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pcompress -p ...
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Attempt Rabin fingerprinting based deduplication on chunks:
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pcompress -D ...
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pcompress -D -r ... - Do NOT split chunks at a rabin boundary. Default is to split.
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Perform Delta Encoding in addition to Exact Dedup:
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pcompress -E ... - This also implies '-D'.
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Number of threads can optionally be specified: -t <1 - 256 count>
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Pass '-M' to display memory allocator statistics
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Pass '-C' to display compression statistics
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Examples
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========
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Compress "file.tar" using bzip2 level 6, 64MB chunk size and use 4 threads. In
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addition perform exact deduplication and delta compression prior to compression.
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pcompress -D -E -c bzip2 -l6 -s64m -t4 file.tar
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Compress "file.tar" using extreme compression mode of LZMA and a chunk size of
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of 1GB. Allow pcompress to detect the number of CPU cores and use as many threads.
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pcompress -c lzma -l14 -s1g file.tar
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