Messages in this thread | | | Date | Tue, 17 Jan 2012 10:07:46 +0100 | From | David Sterba <> | Subject | Re: Updated btrfs/crypto snappy interface ready for merging |
| |
On Thu, Jan 12, 2012 at 04:28:47PM -0800, Andi Kleen wrote: > Here's a slightly updated version of the BTRFS snappy interface. > snappy is a faster compression algorithm that provides similar > compression as LZO, but generally better performance.
Recently the LZ4 method showed up on the real-time compression scene
http://fastcompression.blogspot.com/p/lz4.html (homepage) http://code.google.com/p/lz4/ (source repo)
it has comparable performance and compression ratio to snappy. Quoting from the source repo main page:
Name Ratio C.speed D.speed LZ4 (r41) 2.08 319 1070 LZO 2.05 1x_1 2.07 318 466 Snappy 1.0.4 2.02 242 683
My own benchmarking confirms that lz4 is has a bit faster decompression, but what is a big difference from snappy is it's memory consumption for compression: * 32kb for unbounded chunksize * 16kb for chunksize < 64k (a tuned compression)
No additional memory is needed for decompression in both snappy and lz4. With a minor tweak and chunksize < 4G the context size could be reduced to 16k as well.
There is also LZ4HC, "high compression" mode, which maintains same binary format, but the compression ratio is better.
http://code.google.com/p/lz4hc/
Usecase: There could be the fast version used transparently and the -hc version could be allowed for the 'fi defrag' command in order to recompress selected files.
LZ4 is written in C and it's BSD, LZ4HC is L-GPL. There is some space for improvements in the code, but as it's good already as it stands now.
david
| |