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Posted to issues@hive.apache.org by "Jason Xu (Jira)" <ji...@apache.org> on 2019/11/14 13:20:00 UTC

[jira] [Assigned] (HIVE-22495) Parquet count(*) read in all data

     [ https://issues.apache.org/jira/browse/HIVE-22495?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Jason Xu reassigned HIVE-22495:
-------------------------------


> Parquet count(*) read in all data
> ---------------------------------
>
>                 Key: HIVE-22495
>                 URL: https://issues.apache.org/jira/browse/HIVE-22495
>             Project: Hive
>          Issue Type: Bug
>          Components: Reader
>    Affects Versions: 2.3.4
>            Reporter: Jason Xu
>            Assignee: Jason Xu
>            Priority: Major
>
> Running a hive query on a Parquet table
> select count(*) from t
> The query read in all data (all columns) instead of just metadata.
> For comparison, hive 0.13 and Spark read in much less data.
>  
> ||engine||HDFS data read||
> |Hive 2.3.4|          452.9 MB|
> |Hive 0.13|            22.5 KB|
> |Spark|            41.6 KB|
>  
> Seems cause is that Parquet read support fall back to file schema if indexColumnsWanted is empty.
>  
>  
>  



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