Find the longest match in the suffix-sorted array #6
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Fixes clearlinux#2 The current implementation performs a binary search through the suffix-sorted array to find byte sequence matches between old and new files. However, the algorithm is not optimal when it repeatedly matches very short strings, leading to performance issues as reported in issue clearlinux#2. This commit changes the algorithm to consider *all* matches encountered during the binary search and choose the longest of these matches. The overall performance impact is yet to be determined, but it appears to yield a small percentage increase in diff creation time (expected) and a large percentage *decrease* for the case of diffing the files from issue clearlinux#2. In my testing, the creation time there decreases from approx 64 minutes to 4.5 seconds. Signed-off-by: Patrick McCarty <patrick.mccarty@intel.com>
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+1, I think the large decrease in diff creation times for files from issue #2 is a good tradeoff for the small increase seen for most files. It should also be mentioned that patch times are faster as a result of the greater match lengths (paraphrasing @phmccarty here). |
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(revisiting this now) I was concerned about the small performance increase for the general case, but the tradeoff for vastly improved performance for certain special cases (e.g. #2) is acceptable for now. I can iterate from this point. |
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Is there a notable difference in memory consumption during runs before/after this change? |
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Fixes #2
The current implementation performs a binary search through the suffix-sorted array to find byte sequence matches between old and new files. However, the algorithm is not optimal when it repeatedly matches very short strings, leading to performance issues as reported in issue #2 .
This commit changes the algorithm to consider all matches encountered during the binary search and choose the longest of these matches.
The overall performance impact is yet to be determined, but it appears to yield a small percentage increase in diff creation time (expected) and a large percentage decrease for the case of diffing the files from issue #2. In my testing, the creation time there decreases from approx 64 minutes to 4.5 seconds.