Oodle Mermaid

Mermaid is a new compressor with a unique balance of space and speed. Mermaid is very close to LZ4 decode speeds, while usually beating Zlib compression ratios.

There's really nothing even close. It's way beyond what was previously thought possible.

Mermaid supports unbounded distance match references. This is part of how it gets such high compression. It does so in a new way which reduces the speed penalty normally incurred by large-window LZ's.

Mermaid almost always compresses better than ZLib. The only exception is on small files, less than 32k or so. The whole Oceanic Bestiary family is best suited to files over 64k. They work fine on smaller files, but they lose their huge advantage. It's always best to combine small files into larger units for compression, particularly so with these compressors.

There's not really any single compressor to compare Mermaid to. What we can do is compare vs. Zlib's compression ratio and LZ4's speed. A kind of mythological hybrid like a Chimera, the head of a Zlib and the legs of an LZ4.

Tests on Win64 (Core i7-3770 3.4 GHz) :

Silesia :

On Silesia, Mermaid is just slightly slower than LZ4 but compresses much more than Zlib !!

PD3D :

On PD3D, Mermaid gets almost exactly the compression level of ZLib but the decode speed of LZ4. Magic! It turns out you *can* have your cake and eat it too.

Game Test Set :

lzt99 :

Mermaid really compresses well on lzt99 ; not only does it kill Zlib, it gets close to high compression LZ-Huffs like RAR. (RAR gets 10826108 , Mermaid 10838455 bytes).

Seven :

Because of the space-speed optimizing nature of Mermaid, it will make decisions to be slower than LZ4 when it can find big compression gains. For example if you look at the individual files of the "Seven" test set below - Mermaid is typically right around the same speed as LZ4 or even faster (baby7,dds7,exe7,game7,wad7 - all same speed or faster than LZ4). On a few files it decides to take an encoding slower to decode than LZ4 - model7,enwik7, and records7. The biggest differences are enwik7 and records7, but if you look at the compression ratios - those are all the files where it found huge size differences over LZ4. It has an internal exchange rate for time vs. bytes that it must meet in order to take that encoding, trying to optimize for its space-speed target usage.

Seven files :

Silesia              : Mermaid    : 3.571 to 1 : 2022.038 MB/s
Silesia              : lz4hc      : 2.723 to 1 : 2267.021 MB/s
Silesia              : zlib9      : 3.128 to 1 : 358.681 MB/s

GameTestSet          : Mermaid    : 2.284 to 1 : 2718.095 MB/s
GameTestSet          : lz4hc      : 1.776 to 1 : 3226.887 MB/s
GameTestSet          : zlib9      : 1.992 to 1 : 337.986 MB/s

lzt99                : Mermaid    : 2.279 to 1 : 2283.278 MB/s
lzt99                : lz4hc      : 1.669 to 1 : 2605.366 MB/s
lzt99                : zlib9      : 1.883 to 1 : 309.304 MB/s

PD3D                 : Mermaid    : 2.875 to 1 : 2308.830 MB/s
PD3D                 : lz4hc      : 2.238 to 1 : 2369.666 MB/s
PD3D                 : zlib9      : 2.886 to 1 : 382.349 MB/s

Seven                : Mermaid    : 2.462 to 1 : 2374.212 MB/s
Seven                : lz4hc      : 2.000 to 1 : 2521.296 MB/s
Seven                : zlib9      : 2.329 to 1 : 315.370 MB/s

See the index of this series of posts for more information : Introducing Oodle Mermaid and Selkie . For more about Oodle visit RAD Game Tools