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From "Sahil Takiar (JIRA)" <>
Subject [jira] [Commented] (HIVE-15114) Remove extra MoveTask operators
Date Thu, 03 Nov 2016 17:01:58 GMT


Sahil Takiar commented on HIVE-15114:

Scratch that, probably won't work since Conditional Tasks aren't resolved until they actually
start running.

> Remove extra MoveTask operators
> -------------------------------
>                 Key: HIVE-15114
>                 URL:
>             Project: Hive
>          Issue Type: Sub-task
>          Components: Hive
>    Affects Versions: 2.1.0
>            Reporter: Sahil Takiar
>            Assignee: Sergio Peña
> 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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