pixz VS rapidgzip

That's really confusing since `pixz` exists and its "pixie" pronunciation actually works

https://github.com/vasi/pixz

pixz (https://github.com/vasi/pixz) is a nice parallel xz that additionally creates an index of tar files so you can decompress individual files. I wonder if dpkg could be extended to do something similar.

There's pixz, which indexes the tarball, allowing listing/extracting individual paths without decompressing the whole thing.

Also relevant is pixz [1] which can do parallel LZMA/XZ decompression as well as tar file indexing.

[1] https://github.com/vasi/pixz

Yes, it's as easy as installing pixz with symlinks pointing to xz (I think Debian even does this automatically as part of its post-installation scripts).

pixz - Parallel, indexed xz compressor. BSD-2-Clause

Not quite what you're asking, but if you're a 7-Zip fan and on Linux, you might be interested in pixz.

I also did benchmarks with zlib and libarchivemount via their library interface here [0]. It has been a while that I have run them, so I forgot. Unfortunately, I did not add libdeflate.

[0] https://github.com/mxmlnkn/rapidgzip/blob/master/src/benchma...

Hi, author here.

You are right in the index being the easy-mode. Over the years there have been lots of implementations trying to add an index like that to the gzip metadata itself or as a sidecar file, with bgzip probably being the most known one. None of them really did stick, hence the necessity for some generic multi-threaded decompressor. A probably incomplete list of such implementations can be found in this issue: https://github.com/mxmlnkn/rapidgzip/issues/8

The index makes it so easy that I can simply delegate decompression to zlib. And since paper publication I've actually improved upon this by delegating to ISA-l / igzip instead, which is twice as fast. This is already in the 0.8.0 release.

As derived from table 1, the false positive rate is 1 Tbit / 202 = 5 Gbit or 625 MB for deflate blocks with dynamic Huffman code. For non-compressed blocks, the false positive rate is roughly one per 500 KB, however non-compressed blocks can basically be memcpied or skipped over and then the next deflate header can be checked without much latency. On the other hand, for dynamic blocks, the whole block needs to be decompressed first to find the next one. So the much higher false positive rate for non-compressed blocks doesn't introduce that much overhead.

I have some profiling built into rapidgzip, which is printed with -v, e.g., rapidgzip -v -d -o /dev/null 20xsilesia.tar.gz :

    Time spent in block finder              : 0.227751 s

I have not only implemented parallel decompression but also random access to offsets in the stream with https://github.com/mxmlnkn/pragzip I did some benchmarks on some really beefy machines with 128 cores and was able to reach almost 20 GB/s decompression bandwidth. The single-core decoder has lots of potential for optimization because I had to write it from scratch, though.

Decompression of arbitrary gzip files can be parallelized with pragzip: https://github.com/mxmlnkn/pragzip

At the very least you are duplicating logic without the exception. The check for eof has to be done implicitly anyway inside read because it has to fill the bit buffer with data from the byte buffer or the byte buffer with data from the file. And if both fail, then we already know the result of eof, so no need to duplicate checking for eof in the outer read calling loop.

Here is the full commit with ad-hoc benchmark results in the commit message:

https://github.com/mxmlnkn/pragzip/commit/0b1af498377838c30f...

and here the benchmarks I ran at that time:

https://github.com/mxmlnkn/pragzip/blob/0b1af498377838c30fea...

As you can see, it's part of my random-seekable multi-threaded gzip and bzip2 parallel decompression libraries.

What you can also see in the commit message is that it wasn't a 50% time reduction but a 50% bandwidth increase, which would translate to a 30% time reduction. It seems I remembered that partly wrong. But it still was a significant optimization for me.