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https://issues.apache.org/jira/browse/HIVE-15114?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15705658#comment-15705658
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Aihua Xu commented on HIVE-15114:
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The patch looks good to me. +1.
> Remove extra MoveTask operators from the ConditionalTask
> --------------------------------------------------------
>
> Key: HIVE-15114
> URL: https://issues.apache.org/jira/browse/HIVE-15114
> Project: Hive
> Issue Type: Sub-task
> Components: Hive
> Affects Versions: 2.1.0
> Reporter: Sahil Takiar
> Assignee: Sergio Peña
> Attachments: HIVE-15114.3.patch, HIVE-15114.4.patch,
> HIVE-15114.5.patch, HIVE-15114.6.patch, HIVE-15114.WIP.1.patch,
> HIVE-15114.WIP.2.patch
>
>
> When running simple insert queries (e.g. {{INSERT INTO TABLE ... VALUES
> ...}}) there an extraneous {{MoveTask}s is created.
> This is problematic when the scratch directory is on S3 since renames require
> copying the entire dataset.
> For simple queries (like the one above), there are two MoveTasks. The first
> one moves the output data from one file in the scratch directory to another
> file in the scratch directory. The second MoveTask moves the data from the
> scratch directory to its final table location.
> The first MoveTask should not be necessary. The goal of this JIRA it to
> remove it. This should help improve performance when running on S3.
> It seems that the first Move might be caused by a dependency resolution
> problem in the optimizer, where a dependent task doesn't get properly removed
> when the task it depends on is filtered by a condition resolver.
> A dummy {{MoveTask}} is added in the
> {{GenMapRedUtils.createMRWorkForMergingFiles}} method. This method creates a
> conditional task which launches a job to merge tasks at the end of the file.
> At the end of the conditional job there is a MoveTask.
> Even though Hive decides that the conditional merge job is no needed, it
> seems the MoveTask is still added to the plan.
> Seems this extra {{MoveTask}} may have been added intentionally. Not sure why
> yet. The {{ConditionalResolverMergeFiles}} says that one of three tasks will
> be returned: move task only, merge task only, merge task followed by a move
> task.
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