[jira] [Commented] (DRILL-4122) Create unit test suite for checking quality of hashing for hash based operators

["Parth Chandra (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/DRILL-4122?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15023091#comment-15023091 ] 

Parth Chandra commented on DRILL-4122:
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https://code.google.com/p/smhasher/    (Unfortunately in C)

It might also be a good idea to evaluate other hash methods.



> Create unit test suite for checking quality of hashing for hash based operators
> -------------------------------------------------------------------------------
>
>                 Key: DRILL-4122
>                 URL: https://issues.apache.org/jira/browse/DRILL-4122
>             Project: Apache Drill
>          Issue Type: Bug
>          Components: Functions - Drill
>    Affects Versions: 1.3.0
>            Reporter: Aman Sinha
>
> We have encountered substantial skew in the hash based operators (hash distribution, hash aggregation, hash join) for certain data sets.  Two such issues are DRILL-2803, DRILL-4119.   
> It would be very useful to have a unit test suite to test the quality of hashing.  
> The number of combinations is large: num_data_types x nullability x num_hash_function_types (32bit, 64bit, AsDouble variations). Plus, the nature of the data itself.   We would have to be judicious about picking a reasonable subset of this space.   We should also look at open source test suites in this area. 



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