Thursday, December 2, 2010

Fusion searches - segments & sequences fully integrated

Finally, after spending quite some time at testing a few different directions (more on this in later notes), i finally had enough time and focus to generalize Fusion for any stream of any character.
I opted for the easy way, by extending the table listing existing segments within range. I had another scheme in mind, with the advantage of being memory-less, albeit at unknown performance cost. Maybe for another version.

Nevertheless. I end up with some usable results, and they  are quite promising.
As a usual "raw" efficiency measure, i counted the number of comparisons here below :

                       MMC  Segment  Fusion   Improvement
Calgary 64K Searches  20.3M  6.55M    5.54M      18%
Firefox 64K Searches  70.3M  47.1M    41.9M      12%
Enwik8  64K Searches   188M   187M     187M       0%

Calgary 512K Searches 34.2M  14.6M    10.9M      34%
Firefox 512K Searches  153M   121M    92.1M      31%
Enwik8  512K Searches  435M   435M     434M       0%

Calgary 4M Searches   38.7M  18.5M    14.2M      30%
Firefox 4M Searches    271M   308M     182M      69%
Enwik8  4M Searches    753M   758M     751M       1%

Now, this is satisfactory. Note how Firefox greatly benefits from fusion search support for "non-zero" bytes. Calgary, which mostly contains streams of zero, achieves a little gain compared to Fusion0. Enwik8 hardly contains any stream at all, and therefore benefits the least.

But the tendency is what matters here. The larger the search window, the better the benefit. Firefox is quite impressive at 4M, keeping in consideration that about 65M comparisons (more than one third of total) are just collisions.

And finally, results are now always better than with good old MMC alone, whatever the file and search window size. Objective reached.

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