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From "Mostafa Mokhtar" <mmokh...@hortonworks.com>
Subject Re: Review Request 25179: HIVE-7905: CBO: more cost model changes
Date Tue, 02 Sep 2014 21:02:37 GMT

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This is an automatically generated e-mail. To reply, visit:
https://reviews.apache.org/r/25179/#review52079
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ql/src/java/org/apache/hadoop/hive/ql/optimizer/optiq/stats/HiveRelMdRowCount.java
<https://reviews.apache.org/r/25179/#comment90814>

    My concern is that the computation of selectivity doesn't take into account differences
in NDV which can result in under estimation.



ql/src/java/org/apache/hadoop/hive/ql/optimizer/optiq/stats/HiveRelMdUniqueKeys.java
<https://reviews.apache.org/r/25179/#comment90816>

    Currently NDV in the stats is not accurate.
    As you mentioned max(col) - min(col) is more accurate, hence we are less likely to see
this code in effect due to inaccuracies in NDV.
    Is it possible to add some logging statements for : Table name, column name, row count,
NDV , min and max ?


- Mostafa Mokhtar


On Sept. 2, 2014, 8:23 p.m., Harish Butani wrote:
> 
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> This is an automatically generated e-mail. To reply, visit:
> https://reviews.apache.org/r/25179/
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> 
> (Updated Sept. 2, 2014, 8:23 p.m.)
> 
> 
> Review request for hive, Gunther Hagleitner, John Pullokkaran, and Mostafa Mokhtar.
> 
> 
> Repository: hive-git
> 
> 
> Description
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> 
> CBO: more cost model changes
> 
> 
> Diffs
> -----
> 
>   ql/src/java/org/apache/hadoop/hive/ql/optimizer/optiq/HiveDefaultRelMetadataProvider.java
2c08772 
>   ql/src/java/org/apache/hadoop/hive/ql/optimizer/optiq/stats/HiveRelMdRowCount.java
PRE-CREATION 
>   ql/src/java/org/apache/hadoop/hive/ql/optimizer/optiq/stats/HiveRelMdSelectivity.java
df70de2 
>   ql/src/java/org/apache/hadoop/hive/ql/optimizer/optiq/stats/HiveRelMdUniqueKeys.java
PRE-CREATION 
>   ql/src/java/org/apache/hadoop/hive/ql/parse/SemanticAnalyzer.java 6c293c8 
> 
> Diff: https://reviews.apache.org/r/25179/diff/
> 
> 
> Testing
> -------
> 
> existing tests.
> 
> 
> Thanks,
> 
> Harish Butani
> 
>


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