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https://issues.apache.org/jira/browse/TEZ-1522?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14119672#comment-14119672
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Rajesh Balamohan commented on TEZ-1522:
---------------------------------------
Update: Patch for TEZ-1494 would not completely solve the issue listed here.
I was able to simulate out of order execution scenario with the patch by having
R3->M5 via Scatter_Gather and M7->M5 via broadcast (Instead of having 2
broadcast edges listed in this JIRA).
> Scheduling can result in out of order execution and slowdown of upstream work
> -----------------------------------------------------------------------------
>
> Key: TEZ-1522
> URL: https://issues.apache.org/jira/browse/TEZ-1522
> Project: Apache Tez
> Issue Type: Bug
> Reporter: Rajesh Balamohan
> Assignee: Rajesh Balamohan
> Priority: Critical
> Labels: performance
> Attachments: TEZ-1522.am.log.gz, task_runtime.svg
>
>
> M2 M7
> \ /
> (sg) \ /
> R3 / (b)
> \ /
> (b) \ /
> \ /
> M5
> |
> R6
> Plz refer to the attachment (task runtime SVG). In this case, M5 got
> scheduled much earlier than R3 (green color in the diagram) and retained lots
> of containers.
> R3 got less containers to work with.
> Attaching the output from the status monitor when the job ran; Map_5 has
> taken up almost all of cluster resource, whereas Reducer_3 got fraction of
> the capacity.
> Map_2: 1/1 Map_5: 0(+373)/1000 Map_7: 1/1 Reducer_3: 0/8000
> Reducer_6: 0/1
> Map_2: 1/1 Map_5: 0(+374)/1000 Map_7: 1/1 Reducer_3: 0/8000
> Reducer_6: 0/1
> Map_2: 1/1 Map_5: 0(+374)/1000 Map_7: 1/1 Reducer_3: 0(+1)/8000
> Reducer_6: 0/1
> ....
> Map_2: 1/1 Map_5: 0(+374)/1000 Map_7: 1/1 Reducer_3:
> 14(+7)/8000 Reducer_6: 0/1
> Map_2: 1/1 Map_5: 0(+374)/1000 Map_7: 1/1 Reducer_3:
> 63(+14)/8000 Reducer_6: 0/1
> Map_2: 1/1 Map_5: 0(+374)/1000 Map_7: 1/1 Reducer_3:
> 159(+22)/8000 Reducer_6: 0/1
> Map_2: 1/1 Map_5: 0(+374)/1000 Map_7: 1/1 Reducer_3:
> 308(+29)/8000 Reducer_6: 0/1
> ...
> Creating this JIRA as a placeholder for scheduler enhancement. One
> possibililty could be to
> schedule lesser number of tasks in downstream vertices, based on the
> information available for the upstream vertex.
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