![]() Various command shortcuts exist, such as lzma (for xz -format=lzma), unxz (for xz -decompress analogous to gunzip) and xzcat (for unxz -stdout analogous to zcat) liblzma, a software library with an API similar to zlib.xz, the command-line compressor and decompressor (analogous to gzip).XZ Utils consists of two major components: Compression can be much slower than gzip, and is slower than bzip2 for high levels of compression, and is most useful when a compressed file will be used many times. Decompression speed is higher than bzip2, but lower than gzip. In most cases, xz achieves higher compression rates than alternatives like gzip and bzip2. XZ Utils started as a Unix port of Igor Pavlov's LZMA- SDK that has been adapted to fit seamlessly into Unix environments and their usual structure and behavior. For compression/decompression the Lempel–Ziv–Markov chain algorithm (LZMA) is used. XZ Utils (previously LZMA Utils) is a set of free software command-line lossless data compressors, including the programs lzma and xz, for Unix-like operating systems and, from version 5.0 onwards, Microsoft Windows. Beating the compression performance of xz, or has.Clarifications to xz compression article.Measuring execution performance of C++ exceptions.Using a smart card for decryption from the command.A Python extension module using C, C++, FORTRAN an.Testing exception vs error code behaviour with rea.I hope pixz does enough of what you need! Reply Delete * pixz is already available in repositories for major distributions (Debian and derivatives, Fedora, OpenSuSE, MacPorts, homebrew). * pixz supports streaming operation for basic compression/decompression, like tradition Unix tools. Putting all the metadata together in JPAK is a good idea-was it inspired by squashfs? * pixz still has metadata interleaved with file data. * pixz uses fixed-size blocks of data (similar to JPAK), so it retains a good compression ratio even as it allows random access. Yet it's fully backwards-compatible with other xz and tarball tools. * pixz supports random access inside tarballs, by maintaining an index of where each file lives. * pixz also *decompresses* in parallel, which I believe no other tool supports. * pixz does xz compression in parallel, like a bunch of other projects do. ![]() Hi Jussi, have you looked at my project pixz? It can provide C-compatible bindings, has no garbage collector but has a very nice dependency management system (Cargo), which easily allows you to depend on small libraries ("crates") like "byteorder" which allows for endianness-aware reading and writing of numbers, but does not include a kitchen sink. This may be a pain in C++, but nobody said you must use C++. Much of your code seems to be boilerplate (e.g. If you want to be serious about this, please do some research. Encode every value as a difference to a similar (or at least the previous) value. If you have two uids, you need only one bit per file to store it. For example, if you only have one uid and gid, you don't need to store it per file at all. Your solution can also be massively improved! Look at standard design techniques for compression. I get a 120MB squashfs for Linux 4.9.įor the data layout part you are right, tar metadata layout is not optimal for compression. It also supports using LZMA via a parameter. xz uses LZMA2, which is capable of multi-threading.įor truly random access on compressed files, look at squashfs. The man page of xz has two parts you really should read: "-block-size" and "-threads". Even in this case parallel decompression is not possible. There are some attempts to work around this, such as pigz, but they just chop the full file into constant sized blocks and compress them in parallel. This was not really an issue in the seventies, but nowadays even a Raspberry Pi has four cores. Compression and decompression are inherently serial operations. This is unfortunate in itself but it has an even bigger downside. Accessing byte n requires unpacking every byte from the beginning of the file. Wikipedia has further details.Ĭompression makes this even worse. This is a simple and reliable format but it has a big downside: individual entries can not be accessed without processing the entire file from the beginning. It consists of consecutive file metadata and content pairs. Basically it is a stream format for describing files. It does one thing and it does it quite well. It has been in use, basically unchanged, since 1979.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |