Bikas Saha created MAPREDUCE-4893:
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Summary: MR AppMaster can do sub-optimal assignment of containers
to map tasks leading to poor node locality
Key: MAPREDUCE-4893
URL: https://issues.apache.org/jira/browse/MAPREDUCE-4893
Project: Hadoop Map/Reduce
Issue Type: Bug
Reporter: Bikas Saha
Assignee: Bikas Saha
Fix For: 3.0.0
Say the MR AppMaster asks the RM for 3 containers on nodes n1, n2 and n3. There
are 10 node n1-n10 in the same rack. The RM can give it allocated containers in
the list order n5, n2, n1. The way AM map->container assignment happens, the AM
will try to assign node local maps to n5, failing which it will assign rack
local maps to n5. These rack local maps could be node local on n2 and n1 and
would have been assigned to containers on n1 and n2 if the AM had not made an
early rack local match for them on n5. This can lead to poor locality.
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