hadoop-mapreduce-issues mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From "Rahul Jain (JIRA)" <j...@apache.org>
Subject [jira] [Created] (MAPREDUCE-4560) Job can get stuck in a deadlock between mappers and reducers for low values of mapreduce.job.reduce.slowstart.completedmaps (<<1)
Date Wed, 15 Aug 2012 23:34:38 GMT
Rahul Jain created MAPREDUCE-4560:
-------------------------------------

             Summary: Job can get stuck in a deadlock between mappers and reducers for low
values of mapreduce.job.reduce.slowstart.completedmaps (<<1)
                 Key: MAPREDUCE-4560
                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-4560
             Project: Hadoop Map/Reduce
          Issue Type: Bug
            Reporter: Rahul Jain
             Fix For: 2.0.0-alpha


This issue has been seen with MapReduceV2, never with MapReduceV1 in our lab systems.

The parameter mapreduce.job.reduce.slowstart.completedmaps=0.05 (the default value).

We found Application master stuck in a deadlock between mappers and reducers with no progress
in the job; the sequence appears to be:

1. Initial available map/reduce slots were allocated to mappers
2. Once mappers made progress and few of them completed, reducers started occupying few of
the slots due to low values of above config param.
3. The scheduler appears to not give priority to mappers over reducers; after a while in our
system we saw all slots occupied by reducers.
4. Since there were still mapper tasks not yet assigned any slot, the map phase never completed.
5. The system entered a deadlock state where reducers occupy all available slots, but are
waiting for mappers to be complete; mappers cannot move forward because of no slot available.

The workaround in our system was to set 
mapreduce.job.reduce.slowstart.completedmaps=1 and the issue was no longer seen.

--
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

        

Mime
View raw message