[jira] [Assigned] (HIVE-23891) UNION ALL and multiple task attempts can cause file duplication

["László Bodor (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/HIVE-23891?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

László Bodor reassigned HIVE-23891:
-----------------------------------

    Assignee: Zhihua Deng  (was: George Pachitariu)

> UNION ALL and multiple task attempts can cause file duplication
> ---------------------------------------------------------------
>
>                 Key: HIVE-23891
>                 URL: https://issues.apache.org/jira/browse/HIVE-23891
>             Project: Hive
>          Issue Type: Bug
>            Reporter: George Pachitariu
>            Assignee: Zhihua Deng
>            Priority: Major
>              Labels: pull-request-available
>             Fix For: 4.0.0-alpha-2
>
>         Attachments: HIVE-23891.1.patch
>
>          Time Spent: 4h 50m
>  Remaining Estimate: 0h
>
> Hello, 
> the specific scenario when this can happen:
>  - the execution engine is Tez;
>  - speculative execution is on;
>  - the query inserts into a table and the last step is a UNION sql clause;
> The problem is that Tez creates an extra layer of subdirectories when there is a UNION. Later, when deduplicating, Hive doesn't take that into account and only deduplicates folders but not the files inside.
> So for a query like this:
> {code:sql}
> insert overwrite table union_all
>     select * from union_first_part
> union all
>     select * from union_second_part;
> {code}
> The folder structure afterwards will be like this (a possible example):
> {code:java}
> .../union_all/HIVE_UNION_SUBDIR_1/000000_0
> .../union_all/HIVE_UNION_SUBDIR_1/000000_1
> .../union_all/HIVE_UNION_SUBDIR_2/000000_1
> {code}
> The attached patch increases the number of folder levels that Hive will check recursively for duplicates when we have a UNION in Tez.
> Feel free to reach out if you have any questions :).



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