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From "jaehoon ko (JIRA)" <j...@apache.org>
Subject [jira] [Created] (YARN-3856) YARN shoud allocate container that is closest to the data
Date Fri, 26 Jun 2015 07:03:05 GMT
jaehoon ko created YARN-3856:

             Summary: YARN shoud allocate container that is closest to the data
                 Key: YARN-3856
                 URL: https://issues.apache.org/jira/browse/YARN-3856
             Project: Hadoop YARN
          Issue Type: Improvement
          Components: resourcemanager
    Affects Versions: 2.7.0
         Environment: Hadoop cluster with multi-level network hierarchy
            Reporter: jaehoon ko

Currently, given a Container request for a host, ResourceManager allocates a Container with
following priorities (RMContainerAllocator.java):
 - Requested host
 - a host in the same rack as the requested host
 - any host

This can lead to a sub-optimal allocation if Hadoop cluster is deployed on multi-level networked
hosts (which is typical). For example, let's suppose a network architecture with one core
switches, two aggregate switches, four ToR switches, and 8 hosts. Each switch has two downlinks.
Rack IDs of hosts are as follows:
h1, h2: /c/a1/t1
h3, h4: /c/a1/t2
h5, h6: /c/a2/t3
h7, h8: /c/a2/t4

To allocate a container for data in h1, Hadoop first tries h1 itself, then h2, then any of
h3 ~ h8. Clearly, h3 or h4 are better than h5~h8 in terms of network distance and bandwidth.
However, current implementation choose one from h3~h8 with equal probabilities.

This limitation is more obvious when considering hadoop clusters deployed on VM or containers.
In this case, only the VMs or containers running in the same physical host are considered
rack local, and actual rack-local hosts are chosen with same probabilities as far hosts.

The root cause of this limitation is that RMContainerAllocator.java performs exact matching
on rack id to find a rack local host. Alternatively, we can perform longest-prefix matching
to find a closest host. Using the same network architecture as above, with longest-prefix
matching, hosts are selected with the following priorities:
 h3 or h4
 h5 or h6 or h7 or h8

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