hive-dev mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From "Shreepadma Venugopalan (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (HIVE-4435) Column stats: Distinct value estimator should use hash functions that are pairwise independent
Date Mon, 29 Apr 2013 20:48:15 GMT

     [ https://issues.apache.org/jira/browse/HIVE-4435?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Shreepadma Venugopalan updated HIVE-4435:
-----------------------------------------

    Attachment: chart_1(1).png
    
> 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
>            Reporter: Shreepadma Venugopalan
>            Assignee: Shreepadma Venugopalan
>         Attachments: chart_1(1).png, HIVE-4435.1.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.

--
This message is automatically generated by JIRA.
If you think it was sent incorrectly, please contact your JIRA administrators
For more information on JIRA, see: http://www.atlassian.com/software/jira

Mime
View raw message