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From "Hudson (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HIVE-4435) Column stats: Distinct value estimator should use hash functions that are pairwise independent
Date Fri, 07 Jun 2013 06:27:21 GMT

    [ https://issues.apache.org/jira/browse/HIVE-4435?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13677850#comment-13677850
] 

Hudson commented on HIVE-4435:
------------------------------

Integrated in Hive-trunk-h0.21 #2132 (See [https://builds.apache.org/job/Hive-trunk-h0.21/2132/])
    HIVE-4435 : Column stats: Distinct value estimator should use hash functions that are
pairwise independent (Shreepadma Venugopalan via Ashutosh Chauhan) (Revision 1490323)

     Result = FAILURE
hashutosh : http://svn.apache.org/viewcvs.cgi/?root=Apache-SVN&view=rev&rev=1490323
Files : 
* /hive/trunk/ql/src/java/org/apache/hadoop/hive/ql/udf/generic/NumDistinctValueEstimator.java
* /hive/trunk/ql/src/test/results/clientpositive/compute_stats_double.q.out
* /hive/trunk/ql/src/test/results/clientpositive/compute_stats_long.q.out
* /hive/trunk/ql/src/test/results/clientpositive/compute_stats_string.q.out

                
> Column stats: Distinct value estimator should use hash functions that are pairwise independent
> ----------------------------------------------------------------------------------------------
>
>                 Key: HIVE-4435
>                 URL: https://issues.apache.org/jira/browse/HIVE-4435
>             Project: Hive
>          Issue Type: Bug
>          Components: Statistics
>    Affects Versions: 0.10.0, 0.11.0
>            Reporter: Shreepadma Venugopalan
>            Assignee: Shreepadma Venugopalan
>             Fix For: 0.12.0
>
>         Attachments: chart_1(1).png, HIVE-4435.1.patch, HIVE-4435.2.patch
>
>
> The current implementation of Flajolet-Martin estimator to estimate the number of distinct
values doesn't use hash functions that are pairwise independent. This is problematic because
the input values don't distribute uniformly. When run on large TPC-H data sets, this leads
to a huge discrepancy for primary key columns. Primary key columns are typically a monotonically
increasing sequence.

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