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https://issues.apache.org/jira/browse/HADOOP-7777?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13139189#comment-13139189
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Steve Loughran commented on HADOOP-7777:
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-I'll see if I can track down the warning.
-Note that this patch won't be ready to commit until I've got HDFS-2492 happy
with it, which means some way of bridging the NN-instantiated mapper to the
BlockManager. You can't ask the network topology about its rack count as that
will change as it resolves more addresses.
> Implement a base class for DNSToSwitchMapping implementations that can offer
> extra topology information
> -------------------------------------------------------------------------------------------------------
>
> Key: HADOOP-7777
> URL: https://issues.apache.org/jira/browse/HADOOP-7777
> Project: Hadoop Common
> Issue Type: Improvement
> Components: util
> Affects Versions: 0.23.0
> Reporter: Steve Loughran
> Assignee: Steve Loughran
> Attachments: HADOOP-7777-switch.patch, HADOOP-7777-switch.patch
>
>
> HDFS-2492 has identified a need for DNSToSwitchMapping implementations to
> provide a bit more topology information (e.g. whether or not there are
> multiple switches). This could be done by writing an extended interface,
> querying its methods if present and coming up with a default action if there
> is no extended interface.
> Alternatively, we have a base class that all the standard mappings implement,
> with a boolean isMultiRack() method; all the standard subclasses would extend
> this, as could any third party topology provider. The advantage of this
> approach is that it is easier to add new operations without going into a
> multi-interface mess.
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