Mermaid and Selkie are the super-fast-to-decode distant relatives of Kraken. They use some of the same ideas and technology as Kraken, but are independent compressors targetted at even higher speed and lower compression. Mermaid & Selkie make huge strides in what's possible in compression in the high-speed domain, the same way that Kraken did in the high-compression domain.
Mermaid is about twice as fast as Kraken, but with compression around Zlib levels.
Selkie is one of the fastest decompressors in the world, and also gets much more compression than other very-high-speed compressors.
( Oodle is my data compression library that we sell at RAD Game Tools , read more about it there )
Kraken, Mermaid, and Selkie all use an architecture that makes space-speed decisions in the encoder to give the best tradeoff of compressed size vs decoding speed. The three compressors have different performance targets and make decisions suited for each one's usage domain (Kraken favors more compression and will give up some speed, Selkie strongly favors speed, Mermaid is in between).
For detailed information about the new Mermaid and Selkie I've written a series of posts :
cbloom rants Introducing Oodle Mermaid and Selkie
cbloom rants Oodle 2.3.0 All Test Sets
cbloom rants Oodle 2.3.0 ARM Report
cbloom rants Oodle Mermaid and Selkie on PS4
cbloom rants Oodle Mermaid
cbloom rants Oodle Selkie
RAD Game Tools - Oodle Network and Data Compression
Here are some representative numbers on the Silesia test set : (sum of time and size on individual files)
Oodle 2.3.0 Silesia -z6
Kraken : 4.082 to 1 : 999.389 MB/s
Mermaid : 3.571 to 1 : 2022.038 MB/s
Selkie : 3.053 to 1 : 2929.770 MB/s
zstdmax : 4.013 to 1 : 468.497 MB/s
zlib9 : 3.128 to 1 : 358.681 MB/s
lz4hc : 2.723 to 1 : 2267.021 MB/s
on Win64 (Core i7-3770 3.4 GHz)
On Silesia, Mermaid is 5.65X faster to decode than zlib, and gets 14% more compression.
Selkie is 1.3X faster to decode than LZ4 and gets 12% more compression.
Charts on Silesia total : (charts show time and size - lower is better!)
And the speedup chart on Silesia, which demonstrates the space-speed efficiency of a compressor in different usage domains.
Kraken was a huge step in the Pareto frontier that pushed the achievable speedup factor way up beyond what other compressers were doing. There's a pre-Kraken curve where we thought the best possible tradeoff existed, that most other compressors in the world roughly lie on (or under). Kraken set a new frontier way up on its own with nobody to join it; Mermaid & Selkie are the partners on that new curve that have their peaks at higher speeds than Kraken.
You can also see this big jump of the new family very easily in scatter plots, which we'll see in later posts .