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From "Eric Hanson (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HADOOP-10097) Extend JenkinsHash package interface to allow increased code sharing
Date Wed, 13 Nov 2013 19:41:21 GMT
Eric Hanson created HADOOP-10097:
------------------------------------

             Summary: Extend JenkinsHash package interface to allow increased code sharing
                 Key: HADOOP-10097
                 URL: https://issues.apache.org/jira/browse/HADOOP-10097
             Project: Hadoop Common
          Issue Type: Improvement
            Reporter: Eric Hanson
            Assignee: Eric Hanson
            Priority: Minor


I copied some code from org.apache.hadoop.util.hash.JenkinsHash and added it to org.apache.hadoop.hive.ql.exec.vector.expressions.CuckooSetBytes
and modified it slightly because the interface was not quite right for use CuckooSetBytes.


I propose modifying org.apache.hadoop.util.hash.JenkinsHash to provide an additional interface
function:

public int hash(byte[] key, int start, int nbytes, int initval)

This would return a hash value for the sequence of bytes beginning at start and ending at
start + nbytes (exclusive).

The existing interface function in org.apache.hadoop.util.hash.JenkinsHash

public int hash(byte[] key, int nbytes, int initval)

would then be modified to call this new function. The original hash() function does not take
a start parameter, and always assumes the key in byte[] key starts at position 0. This will
expand the use cases for the JenkinsHash package. At that point, the Hive CuckooSetBytes class
can be modified so that it can reference the JenkinsHash package of Hadoop and use it directly,
rather than using a copied and modified version of the code locally.

Existing users of hash(byte[] key, int nbytes, int initval) will then have to pay an extra
function call. If the performance ramifications of this worry anyone, please comment. Alternatives
would be to copy the new version of hash() in entirety into JenkinsHash, or simply not do
this JIRA.




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