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Lei Mao

Machine Learning, Artificial Intelligence, Computer Science.

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Introduction

Sometimes, we would like to compress one or several files into one zipped file or decompress a zipped file. It is very common to use tools such as gzip, zip, or 7zip to create or decompress .gz, .zip, and .7z files, respectively. However, none of these tools on Linux uses multicore and multithread during compression and decompression. When the number of files are large or the file sizes are large, compression and decompression would take a lot of time using single thread.


Pigz is one of the parallel implementation for gzip and zip. Using pigz could greatly save us the time spent on compression and decompression. In this blog post, I would like to briefly discuss how to use pigz.

Pigz

The pigz usages in the blog post are mainly targeted for Ubuntu systems. However, its usages on other Linux operating systems should be almost the same.

Installation

sudo apt update
sudo apt install pigz

Pigz Usages

$ pigz --help
Usage: pigz [options] [files ...]
  will compress files in place, adding the suffix '.gz'. If no files are
  specified, stdin will be compressed to stdout. pigz does what gzip does,
  but spreads the work over multiple processors and cores when compressing.

Options:
  -0 to -9, -11        Compression level (level 11, zopfli, is much slower)
  --fast, --best       Compression levels 1 and 9 respectively
  -b, --blocksize mmm  Set compression block size to mmmK (default 128K)
  -c, --stdout         Write all processed output to stdout (won't delete)
  -d, --decompress     Decompress the compressed input
  -f, --force          Force overwrite, compress .gz, links, and to terminal
  -F  --first          Do iterations first, before block split for -11
  -h, --help           Display a help screen and quit
  -i, --independent    Compress blocks independently for damage recovery
  -I, --iterations n   Number of iterations for -11 optimization
  -J, --maxsplits n    Maximum number of split blocks for -11
  -k, --keep           Do not delete original file after processing
  -K, --zip            Compress to PKWare zip (.zip) single entry format
  -l, --list           List the contents of the compressed input
  -L, --license        Display the pigz license and quit
  -m, --no-time        Do not store or restore mod time
  -M, --time           Store or restore mod time
  -n, --no-name        Do not store or restore file name or mod time
  -N, --name           Store or restore file name and mod time
  -O  --oneblock       Do not split into smaller blocks for -11
  -p, --processes n    Allow up to n compression threads (default is the
                       number of online processors, or 8 if unknown)
  -q, --quiet          Print no messages, even on error
  -r, --recursive      Process the contents of all subdirectories
  -R, --rsyncable      Input-determined block locations for rsync
  -S, --suffix .sss    Use suffix .sss instead of .gz (for compression)
  -t, --test           Test the integrity of the compressed input
  -v, --verbose        Provide more verbose output
  -V  --version        Show the version of pigz
  -Y  --synchronous    Force output file write to permanent storage
  -z, --zlib           Compress to zlib (.zz) instead of gzip format
  --                   All arguments after "--" are treated as files

A typical command for compressing and decompressing a file is like the following:

# Compress
# Always use -k to keep the original file
$ pigz -k -p8 image.png
# Decompress
$ pigz -dk -p8 image.gz

However, vanilla pigz is not very friendly to compressing multiple files into one single file and custom output filepath. We would need to rely on tar, the archive tool.

Tar-Pigz Usages

Using pipe |, we could first archive multiple files or directories first to .tar file and compress using pigz to further generate .tar.gz file.

# Compress
$ tar -cf - data/ index.json | pigz -k -p8 > dataset.tar.gz
# Decompress (Unfortunately two steps)
$ pigz -k -p8 dataset.tar.gz
# Extract file to another directory
$ mkdir -p new_dataset
$ tar -xf dataset.tar -C new_dataset

Alternatively, tar has already integrated custom compressor in its interface, which makes the command looks more clear.

# Compress
$ tar --use-compress-program="pigz -k -p8" -cf dataset.tar.gz data/ index.json
# Extract file to another directory
$ mkdir -p new_dataset
# Decompress
$ tar --use-compress-program="pigz -dk -p8" -xf dataset.tar.gz -C new_dataset

References