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https://issues.apache.org/jira/browse/HADOOP-1985?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12540233
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Hairong Kuang commented on HADOOP-1985:
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Currently in dfs a datanode can get its network location either from the
command line or by running a pluggable script at the startup time. The property
is defined in the default configuration file as below.
<property>
<name>dfs.network.script</name>
<value></value>
<description>
Specifies a script name that print the network location path
of the current machine.
</description>
</property>
> Abstract node to switch mapping into a topology service class used by
> namenode and jobtracker
> ---------------------------------------------------------------------------------------------
>
> Key: HADOOP-1985
> URL: https://issues.apache.org/jira/browse/HADOOP-1985
> Project: Hadoop
> Issue Type: New Feature
> Reporter: eric baldeschwieler
> Assignee: Devaraj Das
>
> In order to implement switch locality in MapReduce, we need to have switch
> location in both the namenode and job tracker. Currently the namenode asks
> the data nodes for this info and they run a local script to answer this
> question. In our environment and others that I know of there is no reason to
> push this to each node. It is easier to maintain a centralized script that
> maps node DNS names to switch strings.
> I propose that we build a new class that caches known DNS name to switch
> mappings and invokes a loadable class or a configurable system call to
> resolve unknown DNS to switch mappings. We can then add this to the namenode
> to support the current block to switch mapping needs and simplify the data
> nodes. We can also add this same callout to the job tracker and then
> implement rack locality logic there without needing to chane the filesystem
> API or the split planning API.
> Not only is this the least intrusive path to building racklocal MR I can ID,
> it is also future compatible to future infrastructures that may derive
> topology on the fly, etc, etc...
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