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Posted to issues@hive.apache.org by "Jesus Camacho Rodriguez (JIRA)" <ji...@apache.org> on 2016/02/18 21:58:18 UTC
[jira] [Work started] (HIVE-13089) Rounding in Stats for equality
expressions
[ https://issues.apache.org/jira/browse/HIVE-13089?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Work on HIVE-13089 started by Jesus Camacho Rodriguez.
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> Rounding in Stats for equality expressions
> ------------------------------------------
>
> Key: HIVE-13089
> URL: https://issues.apache.org/jira/browse/HIVE-13089
> Project: Hive
> Issue Type: Bug
> Components: Statistics
> Affects Versions: 2.1.0
> Reporter: Jesus Camacho Rodriguez
> Assignee: Jesus Camacho Rodriguez
> Attachments: HIVE-13089.patch
>
>
> Currently we divide numRows(long) by countDistinct(long), thus ignoring the decimals. We should do proper rounding.
> This is specially useful for equality expressions over columns whose values are unique. As NDV estimates allow for a certain error, if countDistinct > numRows, we end up with 0 rows in the estimate for the expression.
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