Compression Benchmarks: brotli, gzip, xz, bz2 | Hacker News Reader

Compression Benchmarks: brotli, gzip, xz, bz2

opencpu.org

41 pointsdatajeroen19 comments

"It's weird how there are like two alternate realities of data compression.

"There's people who actually know WTF they're doing. (eg. encode.ru & the DCC's and so on). In that world you have compressors like PAQ, Nanozip, lzturbo, tornado, CCM, ZCM, Zstd, LZ4, BMF, BCIF, gralic, etc. etc.

"Then there's the mainstream world, where people still think gzip is state of the art (or ooh real modern bzip2), and they invent new things like brotli and webp and seem to not pay any attention to that alternate reality where the experts live. They sometimes do good work, but it's just a little odd."

- Charles Bloom, 10-02-15 (http://www.cbloom.com/rambles.html)

There are standard corpuses for compression / decompression. Against a specific README file isn't interesting.

Give me the full results against the standard corpuses (in different sizes).

The biggest fallacy of "compression results" is non-standard data sets.

Edit: spent years in image/video compression under Langdon, involved with JPEG2000, etc.

Do you know a current good comparison?

https://quixdb.github.io/squash-benchmark/

This is used by many -

http://corpus.canterbury.ac.nz

The published results aren't consistent with the general understanding that xz is faster than bzip2 while compressing better even at the lowest settings.

Xz beyond the lowest compression setting quickly enters the realm of diminishing returns, but when even the lowest setting compresses better than bzip2 and is faster in both compression and decompression, there is no reason to use bzip2.

The opencpu post completely ignores the compression setting dimension, presenting an incomplete picture. Xz is shown as consistently the slowest by a wide margin, even relative to bzip2. This is unexpected, xz will be faster in both compression and decompression than bzip2 when using a compression setting appropriate for comparison with bzip2 compression ratios.

Also xz upstream defaults to single threaded. However xz decompression scales pretty much linearly at least up to 4 cores - I wrote a parallel pxzcat to prove that:

http://git.annexia.org/?p=pxzcat.git;a=summary

> Xz beyond the lowest compression setting quickly enters the realm of diminishing returns, but when even the lowest setting compresses better than bzip2 and is faster in both compression and decompression, there is no reason to use bzip2.

Reasons may revolve around other things than compression quality and speed. For instance, it may be that a company has a history of storing archives using a particular archive format. Another would be a desire to communicate with other entities using a format both parties can use.

This blog is intended for the audience of the R programming language. The benchmarks are comparing compression techniques available in R with their default settings, rather than giving a comprehensive review of compression methodology.

> Hence we can conclude

By testing on one file. Furthermore, Brotli "cheats" by having a static dictionary including english words, so it doesn't make sense to compare against general-purpose compressors on the COPYING file.

Its job is to compress html, so at the very least the html-related dictionary contents make a lot of sense.

They are testing compression on a 6849 byte file full of English text. (GPL)

This is a terrible comparison test - first of all, it's biased because of Brotli's built-in dictionary, and the file size is so small that the compression performance might well be overwhelmed by the startup time of each compressor / decompressor. Consider that the compression level of bzip2 (the 1-9 parameter) controls a search block size of 100k-900k - so the input file is far far smaller than even the smallest, worst compression setting.

There are several good example file sets to try compression with, they should be used if you want to do any kind of comparative general testing.

The article explicitly states that it is trying to find out which algorithm is optimal for small text-based documents that are common on the web, such as CSS, JS, and HTML.

The best compression algorithm for small text files might be very different from the best algorithm for large amounts of general data. If your browser needs to decompress 100 separate files in a fraction of a second, startup time does matter.

Fair enough, but if you want to compress CSS, JS and HTML then why not test it on those?

It also depends upon how you are supplying the compressed data. For static files, the compression time might not even matter - the web server can cache all the compressed versions and the compression performance is minimised.

For dynamic data (e.g. the output of a PHP or whatever), you might also want to test how well the compressors handle streaming data, e.g. feeding parts of a page piecemeal into the compressor and directly sending the output to the client packet by packet. Some compression systems handle this extremely badly.

> Brotli decompression is at least as fast as for gzip while significantly improving the compression ratio. The price we pay is that compression is much slower than gzip.

Is it as fast as gzip or slower?

Fast decompression, slower compression.

Would have been useful to do this against Snappy and LZ4.

Both are quiet popular in the Big Data space.

Brotli is a "strong" compression algorithm so it's obviously going to be much slower with much better compression than "light" algorithms like Snappy or LZ4.

What's the Weissman score

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