[contrib] Edit distance match finder#2036
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bimbashrestha merged 1 commit intofacebook:devfrom Mar 23, 2020
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Ping. Should we merge this or leave it out? Both seems reasonable to me. Might be useful if someone ever wants to experiment with edit distance based match finding in the future. |
Cyan4973
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Mar 23, 2020
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I think it's fine to merge it. |
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Turned out to not provide enough utility to make up for the additional CPU usage. Including this in contrib with some light docs in case this becomes interesting again.
The one place where this outperforms zstd-19 for compression ratio consistently is when compressing a small file (<10KB) with a small and similar in content dictionary (a use case which doesn't really exist as far as I can tell). There are very few overlapping matches in those cases so edit distance basically does as good of a job as can be done.
For large files, this is 5-10X slower than zstd-19 and 2-3X worse in terms of compression ratio. I Think most of the loss is in being unable to find overlapping matches.
References:
An O(ND) Difference Algorithm and Its Variations:
http://www.xmailserver.org/diff2.pdf
An Algorithm for Differential File Comparison:
https://www.cs.dartmouth.edu/~doug/diff.pdf
A File Comparison Program:
http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.189.70&rep=rep1&type=pdf
More information and references on diff algorithms on this page:
https://wiki.c2.com/?DiffAlgorithm