dengzhhu653 opened a new pull request, #4479:
URL: https://github.com/apache/hive/pull/4479
…es in union all
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### What changes were proposed in this pull request?
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### Why are the changes needed?
Think of an union all case inserting data to an external table(dynamic
partition):
FS[1] specPath: <staging_dir>/-ext-10000/HIVE_UNION_SUBDIR_1
FS[2] specPath: <staging_dir>/-ext-10000/HIVE_UNION_SUBDIR_2
Finally, the output of FS will locate under the directory:
FS[1]: <staging_dir>/_tmp.-ext-10000/<dynamic_partition>/HIVE_UNION_SUBDIR_1
FS[2]: <staging_dir>/_tmp.-ext-10000/<dynamic_partition>/HIVE_UNION_SUBDIR_2
When the task finishes, FS[1] and FS[2] will call jobClose to move their
output to <staging_dir>/-ext-10000, the MoveTask is responsible for moving it
to the destination table.
https://github.com/apache/hive/blob/81759a105e50b9fd8c66ffbf2920f425a1d7a64c/ql/src/java/org/apache/hadoop/hive/ql/exec/tez/TezTask.java#L679-L689
Before the FS[1] moves the data, it will rename
<staging_dir>/_tmp.-ext-10000 to <staging_dir>/_tmp.-ext-10000.moved,
https://github.com/apache/hive/blob/master/ql/src/java/org/apache/hadoop/hive/ql/exec/Utilities.java#L1453-L1456
FS[1] will only deduplicate the result under the
_tmp.-ext-10000.moved/<dynamic_partition>/HIVE_UNION_SUBDIR_1, and add the
valid output file to `filesKept`, ignore the result under HIVE_UNION_SUBDIR_2
or more...
When it turns to FS[2] to close the operator, as the temp output directory
has already been renamed to `_tmp.-ext-10000.moved`, so the FS[2] will do
nothing.
So this will cause task result duplication, and in some cases, the result
will lose as the `filesKept` only keeps the result of only one branch.
To solve this, one idea is making every FS have his own private temp output
directory. For example:
FS[1]:
<staging_dir>/-ext-10000/_tmp.HIVE_UNION_SUBDIR_1/<dynamic_partition>/HIVE_UNION_SUBDIR_1
FS[2]:
<staging_dir>/-ext-10000/_tmp.HIVE_UNION_SUBDIR_2/<dynamic_partition>/HIVE_UNION_SUBDIR_2
When FS closes, each FS operator only takes care of his own output, and move
the temp output to <staging_dir>/-ext-10000 as it does before, and this method
will bring some performance gain in case renaming to `_tmp.-ext-10000.moved` is
not allowed:
https://github.com/apache/hive/blob/master/ql/src/java/org/apache/hadoop/hive/ql/exec/Utilities.java#L1461-L1462
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### Does this PR introduce _any_ user-facing change?
No
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### Is the change a dependency upgrade?
No
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### How was this patch tested?
Added UT
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