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https://issues.apache.org/jira/browse/MAPREDUCE-5844?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Maysam Yabandeh updated MAPREDUCE-5844:
---------------------------------------
Attachment: MAPREDUCE-5844.patch
I reverted the changes about visibility of existing methods as well as added
synchronization to address findbugs warnings. I went through code with
[~sjlee0] and it seems to us that the current synchronization is enough to
protect the variables. Therefore making the variables AtomicInteger would incur
the extra sync cost with no clear benefit. It could also add confusion about
sync policy in the code. I am submitting the patch with reverted visibilities
and if findbugs complains again I would suggest adding it to the exclude list.
(sorry that findbugs on my laptop seems not be working, will work on that).
About the new location of TestRMContainerAllocator.java, I see that updated by
the patch:
{code}
diff --git
hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-app/src/test/java/org/apache/hadoop/mapreduce/v2/app/TestRMContainerAllocator.java
hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-app/src/test/java/org/apache/hadoop/mapreduce/v2/app/rm/TestRMContainerAllocator.java
similarity index 93%
rename from
hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-app/src/test/java/org/apache/hadoop/mapreduce/v2/app/TestRMContainerAllocator.java
rename to
hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-app/src/test/java/org/apache/hadoop/mapreduce/v2/app/rm/TestRMContainerAllocator.java
{code}
I generated the patch with "git diff trunk --no-prefix". It might be an
inconsistency issue of git with "patch -p0".
> Reducer Preemption is too aggressive
> ------------------------------------
>
> Key: MAPREDUCE-5844
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-5844
> Project: Hadoop Map/Reduce
> Issue Type: Bug
> Reporter: Maysam Yabandeh
> Assignee: Maysam Yabandeh
> Attachments: MAPREDUCE-5844.patch, MAPREDUCE-5844.patch,
> MAPREDUCE-5844.patch, MAPREDUCE-5844.patch, MAPREDUCE-5844.patch,
> MAPREDUCE-5844.patch, MAPREDUCE-5844.patch, MAPREDUCE-5844.patch
>
>
> We observed cases where the reducer preemption makes the job finish much
> later, and the preemption does not seem to be necessary since after
> preemption both the preempted reducer and the mapper are assigned
> immediately--meaning that there was already enough space for the mapper.
> The logic for triggering preemption is at
> RMContainerAllocator::preemptReducesIfNeeded
> The preemption is triggered if the following is true:
> {code}
> headroom + am * |m| + pr * |r| < mapResourceRequest
> {code}
> where am: number of assigned mappers, |m| is mapper size, pr is number of
> reducers being preempted, and |r| is the reducer size.
> The original idea apparently was that if headroom is not big enough for the
> new mapper requests, reducers should be preempted. This would work if the job
> is alone in the cluster. Once we have queues, the headroom calculation
> becomes more complicated and it would require a separate headroom calculation
> per queue/job.
> So, as a result headroom variable is kind of given up currently: *headroom is
> always set to 0* What this implies to the speculation is that speculation
> becomes very aggressive, not considering whether there is enough space for
> the mappers or not.
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