Hadoop Map/Reduce
  1. Hadoop Map/Reduce
  2. MAPREDUCE-4560

Job can get stuck in a deadlock between mappers and reducers for low values of mapreduce.job.reduce.slowstart.completedmaps (<<1)

    Details

    • Type: Bug Bug
    • Status: Resolved
    • Priority: Major Major
    • Resolution: Duplicate
    • Affects Version/s: None
    • Fix Version/s: None
    • Component/s: None
    • Labels:
      None

      Description

      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.

        Issue Links

          Activity

          Hide
          Harsh J added a comment -

          Resolving as Dupe as noted by Rahul above.

          Show
          Harsh J added a comment - Resolving as Dupe as noted by Rahul above.
          Hide
          Rahul Jain added a comment -

          Yes, this issue was found in FIFO scheduler; we can mark it duplicate of MAPREDUCE-4299 once we verify that fix does resolve the issue.

          Show
          Rahul Jain added a comment - Yes, this issue was found in FIFO scheduler; we can mark it duplicate of MAPREDUCE-4299 once we verify that fix does resolve the issue.
          Hide
          Nemon Lou added a comment -

          Do you use the FIFO scheduler?
          If so ,have a look at MAPREDUCE-4299

          Show
          Nemon Lou added a comment - Do you use the FIFO scheduler? If so ,have a look at MAPREDUCE-4299

            People

            • Assignee:
              Unassigned
              Reporter:
              Rahul Jain
            • Votes:
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              Watchers:
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              Dates

              • Created:
                Updated:
                Resolved:

                Development