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From "Jonathan Ellis (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HBASE-1136) HashFunction inadvertently destroys some randomness
Date Tue, 20 Jan 2009 00:39:00 GMT

    [ https://issues.apache.org/jira/browse/HBASE-1136?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12665293#action_12665293
] 

Jonathan Ellis commented on HBASE-1136:
---------------------------------------

How do I run just TestFilter, and how do I get it to tell me what the failure details are?

    [junit] Running org.onelab.test.TestFilter
    [junit] Tests run: 3, Failures: 2, Errors: 0, Time elapsed: 0.019 sec
    [junit] Test org.onelab.test.TestFilter FAILED

not super helpful. :)

> HashFunction inadvertently destroys some randomness
> ---------------------------------------------------
>
>                 Key: HBASE-1136
>                 URL: https://issues.apache.org/jira/browse/HBASE-1136
>             Project: Hadoop HBase
>          Issue Type: Bug
>            Reporter: Jonathan Ellis
>             Fix For: 0.20.0
>
>         Attachments: hash.patch
>
>
> the code
>       for (int i = 0, initval = 0; i < nbHash; i++) {
>         initval = result[i] = Math.abs(hashFunction.hash(b, initval) % maxValue);
>       }
> restricts initval for the next hash to the [0, maxValue) range of the hash indexes returned.
 This is suboptimal, particularly for larger nbHash and smaller maxValue.  Instead, use:
>       for (int i = 0, initval = 0; i < nbHash; i++) {
>         initval = hashFunction.hash(b, initval);
>         result[i] = Math.abs(initval) % maxValue;
>       }

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