Details
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Bug
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Status: Closed
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Major
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Resolution: Fixed
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0.10.0
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None
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None
Description
It might be a good idea to optimize simple union queries containing map-reduce jobs in at least one of the sub-qeuries.
For eg:
a query like:
insert overwrite table T1 partition P1
select * from
(
subq1
union all
subq2
) u;
today creates 3 map-reduce jobs, one for subq1, another for subq2 and
the final one for the union.
It might be a good idea to optimize this. Instead of creating the union
task, it might be simpler to create a move task (or something like a move
task), where the outputs of the two sub-queries will be moved to the final
directory. This can easily extend to more than 2 sub-queries in the union.
This is very useful if there is a select * followed by filesink after the
union. This can be independently useful, and also be used to optimize the
skewed joins –
https://cwiki.apache.org/confluence/display/Hive/Skewed+Join+Optimization.
If there is a select, filter between the union and the filesink, the select
and the filter can be moved before the union, and the follow-up job can
still be removed.
Attachments
Attachments
Issue Links
- depends upon
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- Closed
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- Closed
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- is depended upon by
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HIVE-3380 As a follow up for HIVE-3276, optimize union for dynamic partition queries
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- Closed
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- is related to
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HIVE-8054 Disable hive.optimize.union.remove when hive.execution.engine=spark [Spark Branch]
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- Resolved
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- Closed
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HIVE-3643 Hive List Bucketing - set hive.mapred.supports.subdirectories
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- Closed
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