[jira] [Commented] (HADOOP-7030) new topology mapping implementations

["Steve Loughran (Commented) (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HADOOP-7030?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13213779#comment-13213779 ] 

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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