You are viewing a plain text version of this content. The canonical link for it is here.
Posted to mapreduce-issues@hadoop.apache.org by "Robert Joseph Evans (JIRA)" <ji...@apache.org> on 2012/06/20 22:00:43 UTC
[jira] [Commented] (MAPREDUCE-4358) Reducers are assigned
containers before all maps are assigned containers
[ https://issues.apache.org/jira/browse/MAPREDUCE-4358?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13397825#comment-13397825 ]
Robert Joseph Evans commented on MAPREDUCE-4358:
------------------------------------------------
Isn't that what mapreduce.job.reduce.slowstart.completedmaps is for? If you don't want any reducers to run until all of the maps have finished then you want to set it to 1.0, not the 0.05 that is the default. I think part of the issue is that the default value for mapreduce.job.reduce.slowstart.completedmaps is still set for when map and reduce slots were completely separate. Perhaps this config does not make since any more now that reduce tasks can block map tasks from running. Or perhaps we need another config so that the AM will not fill more than X% of the queue with reduces until all map tasks have completed.
We have taken the rout of setting the slowstart to 1.0 even on our 1.0.2 clusters because it improves the cluster utilization and we have not seen much of a hit to the end to end time of our jobs.
> Reducers are assigned containers before all maps are assigned containers
> ------------------------------------------------------------------------
>
> Key: MAPREDUCE-4358
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-4358
> Project: Hadoop Map/Reduce
> Issue Type: Bug
> Components: mrv2
> Affects Versions: 2.0.0-alpha
> Reporter: Ahmed Radwan
>
> Reducers start to get containers before all maps are. We have seen this issue and it is problematic since if there is no avaialable resources for the remaining maps, the job will just stall where reducers are waiting for mappers which are unable to start because there is no containers available.
--
This message is automatically generated by JIRA.
If you think it was sent incorrectly, please contact your JIRA administrators: https://issues.apache.org/jira/secure/ContactAdministrators!default.jspa
For more information on JIRA, see: http://www.atlassian.com/software/jira