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https://issues.apache.org/jira/browse/TAJO-385?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13849990#comment-13849990
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Hyunsik Choi edited comment on TAJO-385 at 12/17/13 1:52 AM:
-------------------------------------------------------------
This idea is great and will overcome many limits of the query whose an input
data is a number of HDFS blocks. Actually, I love this idea.
In addition, there are some challenges and issues which are somewhat trivial
but must be resolved.
* As I mentioned, this idea requires an alternative to exactly indicate the
execution block's progress.
* The task volume size should be adjustable during one execution block.
** Otherwise, the final task execution wave may be longer due to fewer
assigned workers than available worker.
* It would be great to enable a query master to choose a task scheduler before
executing a certain execution block.
** For table writing, some task scheduler can be chosen, and the previous
task scheduler can be useful for compressed, non-splitable, and
larger-than-blocks files.
was (Author: hyunsik):
This idea is great and will overcome many limits the query whose an input data
is a number of HDFS blocks. Actually, I love this idea.
In addition, there are some challenges and issues which are somewhat trivial
but must be resolved.
* As I mentioned, this idea requires an alternative to exactly indicate the
execution block's progress.
* The task volume size should be adjustable during one execution block.
** Otherwise, the final task execution wave may be longer due to fewer
assigned workers than available worker.
* It would be great to enable a query master to choose a task scheduler before
executing a certain execution block.
** For table writing, some task scheduler can be chosen, and the previous
task scheduler can be useful for compressed, non-splitable, and
larger-than-blocks files.
> Refactoring TaskScheduler to assign multiple fragments
> ------------------------------------------------------
>
> Key: TAJO-385
> URL: https://issues.apache.org/jira/browse/TAJO-385
> Project: Tajo
> Issue Type: Improvement
> Components: query master
> Affects Versions: 0.8-incubating
> Reporter: Jihoon Son
> Assignee: Jihoon Son
> Attachments: TAJO-385.patch, TAJO-385_2.patch, TAJO-385_3.patch
>
>
> In the current implementation, each task processes only one fragment.
> However, processing multiple fragments in a task will increase the query
> processing performance according to the storage layout and the user queries.
> In this issue, TaskScheduler is refactored to enable assigning multiple
> fragments to each task.
> Followings should be contained.
> * Schedule Fragments instead of QueryUnits in TaskScheduler
> ** The QueryUnit creation is postponed until TaskScheduler receives task
> requests from workers.
> ** When TaskScheduler receives task requests from workers, it dynamically
> creates an QueryUnit and assigns one or more fragments.
> ** The fragment scheduling should take into account the disk load balancing.
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