hadoop-mapreduce-issues mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From "Hadoop QA (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (MAPREDUCE-5844) Reducer Preemption is too aggressive
Date Sat, 24 May 2014 00:09:02 GMT

    [ https://issues.apache.org/jira/browse/MAPREDUCE-5844?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14007913#comment-14007913
] 

Hadoop QA commented on MAPREDUCE-5844:
--------------------------------------

{color:red}-1 overall{color}.  Here are the results of testing the latest attachment 
  http://issues.apache.org/jira/secure/attachment/12646359/MAPREDUCE-5844.patch
  against trunk revision .

    {color:green}+1 @author{color}.  The patch does not contain any @author tags.

    {color:red}-1 tests included{color}.  The patch doesn't appear to include any new or modified
tests.
                        Please justify why no new tests are needed for this patch.
                        Also please list what manual steps were performed to verify this patch.

    {color:green}+1 javac{color}.  The applied patch does not increase the total number of
javac compiler warnings.

    {color:green}+1 javadoc{color}.  There were no new javadoc warning messages.

    {color:green}+1 eclipse:eclipse{color}.  The patch built with eclipse:eclipse.

    {color:green}+1 findbugs{color}.  The patch does not introduce any new Findbugs (version
1.3.9) warnings.

    {color:green}+1 release audit{color}.  The applied patch does not increase the total number
of release audit warnings.

    {color:green}+1 core tests{color}.  The patch passed unit tests in hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-app
hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-core.

    {color:green}+1 contrib tests{color}.  The patch passed contrib unit tests.

Test results: https://builds.apache.org/job/PreCommit-MAPREDUCE-Build/4619//testReport/
Console output: https://builds.apache.org/job/PreCommit-MAPREDUCE-Build/4619//console

This message is automatically generated.

> 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
>
>
> 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.



--
This message was sent by Atlassian JIRA
(v6.2#6252)

Mime
View raw message