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https://issues.apache.org/jira/browse/MAPREDUCE-6302?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14940173#comment-14940173
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Jason Lowe commented on MAPREDUCE-6302:
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bq. Aren't all reducers in SHUFFLE phase until all the mappers are done?
No, here's an example scenario:
# All maps complete, all reducers scheduled and some (or all) started
# Some of the reducers, but not all, finish shuffling and proceed to the MERGE
or REDUCE phases
# Node with some map outputs goes down
# Remaining reducers in the SHUFFLE phase or not assigned cannot complete, maps
get retroactively failed for fetch failures, need to launch new map attempts
# At this point we do _not_ want to kill any reducers past the SHUFFLE phase as
they can progress and complete without further interactions for map outputs
> Incorrect headroom can lead to a deadlock between map and reduce allocations
> -----------------------------------------------------------------------------
>
> Key: MAPREDUCE-6302
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-6302
> Project: Hadoop Map/Reduce
> Issue Type: Bug
> Affects Versions: 2.6.0
> Reporter: mai shurong
> Assignee: Karthik Kambatla
> Priority: Critical
> Attachments: AM_log_head100000.txt.gz, AM_log_tail100000.txt.gz,
> log.txt, mr-6302-1.patch, mr-6302-2.patch, mr-6302-3.patch, mr-6302-4.patch,
> mr-6302-prelim.patch, queue_with_max163cores.png, queue_with_max263cores.png,
> queue_with_max333cores.png
>
>
> I submit a big job, which has 500 maps and 350 reduce, to a
> queue(fairscheduler) with 300 max cores. When the big mapreduce job is
> running 100% maps, the 300 reduces have occupied 300 max cores in the queue.
> And then, a map fails and retry, waiting for a core, while the 300 reduces
> are waiting for failed map to finish. So a deadlock occur. As a result, the
> job is blocked, and the later job in the queue cannot run because no
> available cores in the queue.
> I think there is the similar issue for memory of a queue .
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