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https://issues.apache.org/jira/browse/MAPREDUCE-6803?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15632654#comment-15632654
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Junping Du commented on MAPREDUCE-6803:
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Sorry for replying a bit late as busy in travel previously. From my quick
check, most of code is still in YARN side. [~leftnoteasy], May be we should
move back to YARN?
> MR AppMaster should assign container that is closest to the data
> ----------------------------------------------------------------
>
> Key: MAPREDUCE-6803
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-6803
> Project: Hadoop Map/Reduce
> Issue Type: Improvement
> Components: applicationmaster
> Environment: Hadoop cluster with multi-level network hierarchy
> Reporter: jaehoon ko
> Labels: oct16-medium
> Attachments: YARN-3856.001.patch, YARN-3856.002.patch
>
>
> 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:
> h1
> h2
> h3 or h4
> h5 or h6 or h7 or h8
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