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https://issues.apache.org/jira/browse/MAPREDUCE-4827?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13505940#comment-13505940
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Robert Joseph Evans commented on MAPREDUCE-4827:
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That is very interesting. I can see it in java.util.HashMap but it looks like
java.util.Hashtable does not. Assuming that Jenkins comes back with a +1 I am
OK with putting this in. I would like to have some numbers, because this is a
"performance" improvement, but the citation of the code in HashMap.java, which
is almost identical to this patch, is good enough for me. +1
> Increase hash quality of HashPartitioner
> ----------------------------------------
>
> Key: MAPREDUCE-4827
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-4827
> Project: Hadoop Map/Reduce
> Issue Type: Improvement
> Reporter: Radim Kolar
> Attachments: betterhash1.txt
>
>
> hash partitioner is using object.hashCode() for splitting keys into
> partitions. This results in bad distributions because hashCode() quality is
> poor.
> These hashCode() functions are sometimes written by hand (very poor quality)
> and sometimes generated from by commons lang code (poor quality). Applying
> some transformation on top of hashCode() provides better distribution.
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