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https://issues.apache.org/jira/browse/HIVE-21100?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16737980#comment-16737980
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George Pachitariu commented on HIVE-21100:
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Hello [~ekoifman] , thanks for commenting.
The motivation is that some systems in Hadoop, like Impala, cannot read
directories recursively. If a table was created with Hive with subdirectories
and after that, it is queried by Impala, the table will look empty.
I know that this patch will only benefit a few people, that's why it is
disabled by default and I added an option to turn it on.
> Allow flattening of table subdirectories resulted when using TEZ engine and
> UNION clause
> ----------------------------------------------------------------------------------------
>
> Key: HIVE-21100
> URL: https://issues.apache.org/jira/browse/HIVE-21100
> Project: Hive
> Issue Type: Improvement
> Reporter: George Pachitariu
> Assignee: George Pachitariu
> Priority: Minor
> Attachments: HIVE-21100.patch
>
>
> Right now, when writing data into a table with Tez engine and the clause
> UNION ALL is the last step of the query, Hive on Tez will create a
> subdirectory for each branch of the UNION ALL.
> With this patch the subdirectories are removed, and the files are renamed and
> moved to the parent directory.
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