[jira] [Commented] (HIVE-22941) Empty files are inserted into external tables after HIVE-21714

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

    [ https://issues.apache.org/jira/browse/HIVE-22941?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17046467#comment-17046467 ] 

László Bodor commented on HIVE-22941:
-------------------------------------

issue reproduced:
{code}
export QTEST_LEAVE_FILES=true
mvn test -Dtest.output.overwrite=true -Pitests,hadoop-2 -Denforcer.skip=true -pl itests/qtest -Dtest=TestMiniLlapLocalCliDriver -Dqfile=empty_files_non_bucketed.q
...
 lbodor@HW12459  ~/repos/hive   HDP-3.1-maint ●  ls -la itests/qtest/target/localfs/warehouse/t1/000000_0
-rw-r--r--  1 lbodor  staff  0 Feb 25 11:42 itests/qtest/target/localfs/warehouse/t1/000000_0
{code}
https://github.com/abstractdog/hive/commit/7e08a3f654d67848cc2f3a915ebb8294d98e4328


easy fix with acid/mm regression:
https://github.com/abstractdog/hive/commit/8e25b5ce11220e22dbe90958d52c63b52a482931


> Empty files are inserted into external tables after HIVE-21714
> --------------------------------------------------------------
>
>                 Key: HIVE-22941
>                 URL: https://issues.apache.org/jira/browse/HIVE-22941
>             Project: Hive
>          Issue Type: Improvement
>            Reporter: László Bodor
>            Priority: Major
>
> There were multiple patches targeting an issue when INSERT OVERWRITE was ineffective if the input is empty:
> HIVE-18702: INSERT OVERWRITE TABLE doesn't clean the table directory before overwriting
> HIVE-21714: Insert overwrite on an acid/mm table is ineffective if the input is empty
> HIVE-21784: Insert overwrite on an acid (not mm) table is ineffective if the input is empty
> From these patches, HIVE-21714 seems to have a bad effect on external tables, because of this part:
> https://github.com/apache/hive/commit/9a10bc28bee5250c0f667c94a295706a44ed4d7e#diff-9bea2581a1fba611f2c10904857b8823R1268
> The original issue before HIVE-21714 was that the original files in the table survived an insert overwrite, and select(*)>0 was after that. HIVE-21714 seems to enable writing empty files regardless of execution engine / table type, which is not the proper way, as the proper solution would be to completely avoid writing empty files for Tez (this is what HIVE-14014 was about). I found that changing condition to...
> {code}
> if (!isTez && (isStreaming || this.isInsertOverwrite)) 
> {code}
> (which could be an easy solution for external tables) breaks some test cases (both full ACID and MM) in insert_overwrite.q, which could mean they rely somehow on the empty generated file. We need to find a proper solution which is applicable for all table types without polluting external tables.



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