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https://issues.apache.org/jira/browse/MAPREDUCE-7169?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17445997#comment-17445997
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Ahmed Hussein commented on MAPREDUCE-7169:
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bq. Why is denying racks and hosts should be enabled separately? Can you please
elaborate? Currently we try to avoid launching on same rack as old attempt if
there are no containers on diff rack then we try choosing node other than old
attempt node.
Hi [~BilwaST], I second [~jeagles] about separating the rack and the hosts.
Considering the block placement policy on Hadoop, launching the speculative
attempt on a different rack every-time will be a double edge sword. on same
rack will be a double edge sword.
leaving it to be configurable will give much more flexibility to work along
with block placements. Otherwise, the speculative changes will be "All or
nothing: Always run on a different rack or disable it and speculate on the same
node ".
> Speculative attempts should not run on the same node
> ----------------------------------------------------
>
> Key: MAPREDUCE-7169
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-7169
> Project: Hadoop Map/Reduce
> Issue Type: New Feature
> Components: yarn
> Affects Versions: 2.7.2
> Reporter: Lee chen
> Assignee: Bilwa S T
> Priority: Major
> Attachments: MAPREDUCE-7169-001.patch, MAPREDUCE-7169-002.patch,
> MAPREDUCE-7169-003.patch, MAPREDUCE-7169.004.patch, MAPREDUCE-7169.005.patch,
> MAPREDUCE-7169.006.patch, MAPREDUCE-7169.007.patch,
> image-2018-12-03-09-54-07-859.png
>
>
> I found in all versions of yarn, Speculative Execution may set the
> speculative task to the node of original task.What i have read is only it
> will try to have one more task attempt. haven't seen any place mentioning not
> on same node.It is unreasonable.If the node have some problems lead to tasks
> execution will be very slow. and then placement the speculative task to same
> node cannot help the problematic task.
> In our cluster （version 2.7.2，2700 nodes），this phenomenon appear
> almost everyday.
> !image-2018-12-03-09-54-07-859.png!
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