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From "Sudheesh Katkam (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (DRILL-4122) Create unit test suite for checking quality of hashing for hash based operators
Date Mon, 07 Mar 2016 17:06:40 GMT

    [ https://issues.apache.org/jira/browse/DRILL-4122?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15183278#comment-15183278
] 

Sudheesh Katkam commented on DRILL-4122:
----------------------------------------

This is actually a bad measure because there are distributions (other than uniform) with skewness
of 0.

> 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
>            Assignee: Sudheesh Katkam
>
> 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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