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https://issues.apache.org/jira/browse/HADOOP-7030?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13213779#comment-13213779
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Steve Loughran commented on HADOOP-7030:
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With the changes I've been doing to the topology classes (with an optional
abstract base class), these classes would be best if
{{RefreshableDNSToSwitchMapping}} was a subclass of the new
{{AbstractDNSToSwitchMapping}}.
On barrier to any dynamic/refreshable topology class is that the values get
cached. In particular
{{org.apache.hadoop.yarn.util.RackResolver}} checks to see if the mapping is an
instance of {{CachedDNSToSwitchMapping}} -and if not, wraps it in one. the
DNManager doesn't do anything so dramatic - it does do an instance check, but
only to trigger a pre-emptive lookup of all known hosts.
Unless we add flags to {{AbstractDNSToSwitchMapping}} to provide more info
about the resolver (e.g. caching, dynamic, etc), it's probably safest to
subclass {{CachedDNSToSwitchMapping}} and overwrite its resolve method (and
anything else that is useful).
> new topology mapping implementations
> ------------------------------------
>
> Key: HADOOP-7030
> URL: https://issues.apache.org/jira/browse/HADOOP-7030
> Project: Hadoop Common
> Issue Type: New Feature
> Affects Versions: 0.20.1, 0.20.2, 0.21.0
> Reporter: Patrick Angeles
> Assignee: Patrick Angeles
> Attachments: HADOOP-7030-2.patch, HADOOP-7030.patch, topology.patch
>
>
> The default ScriptBasedMapping implementation of DNSToSwitchMapping for
> determining cluster topology has some drawbacks. Principally, it forks to an
> OS-specific script.
> This issue proposes two new Java implementations of DNSToSwitchMapping.
> TableMapping reads a two column text file that maps an IP or hostname to a
> rack ID. Ip4RangeMapping reads a three column text file where each line
> represents a start and end IP range plus a rack ID.
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