Eugene Koifman created HIVE-4679:
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             Summary: WebHCat can deadlock Hadoop if the number of concurrently 
running tasks if higher or equal than the number of mappers
                 Key: HIVE-4679
                 URL: https://issues.apache.org/jira/browse/HIVE-4679
             Project: Hive
          Issue Type: Bug
          Components: HCatalog
    Affects Versions: 0.10.0
            Reporter: Eugene Koifman


o In the current Templeton design, each time a Job is submitted thru the REST 
API (it can be Pig/Hive or MR job), it will consume one Hadoop map slot. Given 
that the number of map slots is finite in the cluster (16 node cluster will 
have 32 map slots), in some circumstances, a user can deadlock the cluster if 
Templeton job submission pipeline takes over all map slots (Templeton map tasks 
will wait for the actual underlying jobs to complete, what will never happen, 
given that Hadoop has no free map slots to schedule new tasks).

o HCat queries use a different mechanism and do not contribute to the deadlock.

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