[GitHub] [kafka] viktorsomogyi edited a comment on pull request #9519: KAFKA-10650: Use Murmur3 instead of MD5 in SkimpyOffsetMap

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viktorsomogyi edited a comment on pull request #9519:
URL: https://github.com/apache/kafka/pull/9519#issuecomment-725539926


   @ijuma I don't think I looked at it but will try it out soon, its speed seems promising. I haven't found a 128bit java implementation but the 64bit in lz4 can be tried out as well. I need to see if the collision rate changes significantly if we reduce the hash size to 64. Theoretically for 100 million distinct keys the probability of collision is 1.469367×10^-23 with 18 bit while for 64 bits it's 2.710138×10^-4 which is significantly larger but it might be enough for the log cleaning use-case.
   
   @junrao I can compile a statistic for this but in my tests the collision rate was on the same level, sometimes slightly better, sometimes slightly worse. The attached image is what I collected manually for the largest test cases but I'll do something more elaborate if you think so :) - but based on this I think yes, the uniqueness of the generated hashes is on the same level.
   ![image](https://user-images.githubusercontent.com/1820518/98840553-3aa37180-2447-11eb-87e4-198856261d23.png)


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