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https://issues.apache.org/jira/browse/HIVE-6041?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Adrian Popescu updated HIVE-6041:
---------------------------------
Description:
The dependency graph among task stages is incorrect for the skewed join
optimized plan. Skewed joins are enabled through "hive.optimize.skewjoin". For
the case that skewed keys do not exist, all the tasks following the common join
are filtered out at runtime.
In particular, the conditional task in the optimized plan maintains no
dependency with the child tasks of the common join task in the original plan.
The conditional task is composed of the map join task which maintains all these
dependencies, but for the case the map join task is filtered out (i.e., no
skewed keys exist), all these dependencies are lost. Hence, all the other task
stages of the query are skipped.
The bug resides in "ql/optimizer/physical/GenMRSkewJoinProcessor.java",
processSkewJoin() function, immediately after the ConditionalTask is created
and its dependencies are set.
was:
The dependency graph among task stages is incorrect for the skewed join
optimized plan. Skewed joins are enabled through "hive.optimize.skewjoin". For
the case that skewed keys do not exist, all tasks following the common join are
filtered out.
In particular, the conditional task in the optimized plan maintains no
dependency with the child tasks of the common join task in the original plan.
The conditional task is composed of the map join task which maintains all these
dependencies, but for the case the map join task is filtered out (i.e., no
skewed keys exist), all these dependencies are lost. Hence, all the other task
stages of the query are skipped.
The bug resides in "ql/optimizer/physical/GenMRSkewJoinProcessor.java",
processSkewJoin() function, immediately after the ConditionalTask is created
and its dependencies are set.
> Incorrect task dependency graph for skewed join optimization
> ------------------------------------------------------------
>
> Key: HIVE-6041
> URL: https://issues.apache.org/jira/browse/HIVE-6041
> Project: Hive
> Issue Type: Bug
> Components: Query Processor
> Affects Versions: 0.11.0
> Environment: Hadoop 1.0.3
> Reporter: Adrian Popescu
> Priority: Critical
>
> The dependency graph among task stages is incorrect for the skewed join
> optimized plan. Skewed joins are enabled through "hive.optimize.skewjoin".
> For the case that skewed keys do not exist, all the tasks following the
> common join are filtered out at runtime.
> In particular, the conditional task in the optimized plan maintains no
> dependency with the child tasks of the common join task in the original plan.
> The conditional task is composed of the map join task which maintains all
> these dependencies, but for the case the map join task is filtered out (i.e.,
> no skewed keys exist), all these dependencies are lost. Hence, all the other
> task stages of the query are skipped.
> The bug resides in "ql/optimizer/physical/GenMRSkewJoinProcessor.java",
> processSkewJoin() function, immediately after the ConditionalTask is created
> and its dependencies are set.
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