Oodle 2.2.0 Kraken Optimal Parse improvements

Oodle 2.2.0 is about to ship, with some improvements to the Kraken optimal parse compression ratios. Compressed size is improved by around 1%. Speed is approximately the same at -z6 (previous max level for Kraken) but there's a new -z7 mode that's slightly slower and even higher compression.

I think we'll continue to find improvements in the optimal parsers over the coming months (optimal parsing is hard!) which should lead to some more tiny gains in the compression ratio in the slow encoder modes.

Silesia , sum of all files

uncompressed : 211,938,580

Kraken 2.1.5 -z6 : 52,366,897
Kraken 2.2.0 -z6 : 51,857,427
Kraken 2.2.0 -z7 : 51,625,488

Oodle Kraken 2.1.5 topped out at -z6 (Optimal2). There's a new -z7 (Optimal3) mode which gets a bit more compression at the cost of a bit of speed, which is why it's on a separate option instead of just part of -z6.

Results on some individual files (Kraken 220 is -z7) :

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"silesia_mozilla"

by ratio:
lzma        :  3.88:1 ,    2.0 enc mb/s ,   63.7 dec mb/s
Kraken 220  :  3.60:1 ,    1.1 enc mb/s ,  896.5 dec mb/s
lzham       :  3.56:1 ,    1.5 enc mb/s ,  186.4 dec mb/s
Kraken 215  :  3.51:1 ,    1.2 enc mb/s ,  928.0 dec mb/s
zstdmax     :  3.24:1 ,    2.8 enc mb/s ,  401.0 dec mb/s
zlib9       :  2.51:1 ,   12.4 enc mb/s ,  291.5 dec mb/s
lz4hc       :  2.32:1 ,   36.4 enc mb/s , 2351.6 dec mb/s

-------------------------------------------------------
"lzt99"

by ratio:
lzma        :  2.65:1 ,    3.1 enc mb/s ,   42.3 dec mb/s
Kraken 220  :  2.53:1 ,    2.0 enc mb/s ,  912.0 dec mb/s
Kraken 215  :  2.46:1 ,    2.3 enc mb/s ,  957.1 dec mb/s
lzham       :  2.44:1 ,    1.9 enc mb/s ,  166.0 dec mb/s
zstdmax     :  2.27:1 ,    3.8 enc mb/s ,  482.3 dec mb/s
zlib9       :  1.77:1 ,   13.3 enc mb/s ,  286.2 dec mb/s
lz4hc       :  1.67:1 ,   30.3 enc mb/s , 2737.4 dec mb/s

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"all_dds"

by ratio:
lzma        :  2.37:1 ,    2.1 enc mb/s ,   40.8 dec mb/s
Kraken 220  :  2.23:1 ,    1.0 enc mb/s ,  650.6 dec mb/s
Kraken 215  :  2.18:1 ,    1.0 enc mb/s ,  684.6 dec mb/s
lzham       :  2.17:1 ,    1.3 enc mb/s ,  127.7 dec mb/s
zstdmax     :  2.02:1 ,    3.3 enc mb/s ,  289.4 dec mb/s
zlib9       :  1.83:1 ,   13.3 enc mb/s ,  242.9 dec mb/s
lz4hc       :  1.67:1 ,   20.4 enc mb/s , 2226.9 dec mb/s

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"baby_robot_shell.gr2"

by ratio:
lzma        :  4.35:1 ,    3.1 enc mb/s ,   59.3 dec mb/s
Kraken 220  :  3.82:1 ,    1.4 enc mb/s ,  837.2 dec mb/s
Kraken 215  :  3.77:1 ,    1.5 enc mb/s ,  878.3 dec mb/s
lzham       :  3.77:1 ,    1.6 enc mb/s ,  162.5 dec mb/s
zstdmax     :  2.77:1 ,    5.7 enc mb/s ,  405.7 dec mb/s
zlib9       :  2.19:1 ,   13.9 enc mb/s ,  332.9 dec mb/s
lz4hc       :  1.78:1 ,   40.1 enc mb/s , 2364.4 dec mb

-------------------------------------------------------
"win81"

by ratio:
lzma        :  2.95:1 ,    2.5 enc mb/s ,   51.9 dec mb/s
lzham       :  2.77:1 ,    1.6 enc mb/s ,  177.6 dec mb/s
Kraken 220  :  2.77:1 ,    1.0 enc mb/s ,  818.0 dec mb/s
Kraken 215  :  2.70:1 ,    1.0 enc mb/s ,  877.0 dec mb/s
zstdmax     :  2.64:1 ,    3.5 enc mb/s ,  417.8 dec mb/s
zlib9       :  2.07:1 ,   16.8 enc mb/s ,  269.6 dec mb/s
lz4hc       :  1.91:1 ,   28.8 enc mb/s , 2297.6 dec mb/s

-------------------------------------------------------
"enwik7"

by ratio:
lzma        :  3.64:1 ,    1.8 enc mb/s ,   79.5 dec mb/s
lzham       :  3.60:1 ,    1.4 enc mb/s ,  196.5 dec mb/s
zstdmax     :  3.56:1 ,    2.2 enc mb/s ,  394.6 dec mb/s
Kraken 220  :  3.51:1 ,    1.4 enc mb/s ,  702.8 dec mb/s
Kraken 215  :  3.49:1 ,    1.5 enc mb/s ,  789.7 dec mb/s
zlib9       :  2.38:1 ,   22.2 enc mb/s ,  234.3 dec mb/s
lz4hc       :  2.35:1 ,   27.5 enc mb/s , 2059.6 dec mb/s

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You can see that encode & decode speed is slightly worse at level -z7 , and compression ratio si improved. (most of the other compression levels have roughly the same decode speed; -z7 enables some special options that can hurt decode speed a bit). Of course even at -z7 Kraken is way faster than anything else comparable!