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https://issues.apache.org/jira/browse/HADOOP-7030?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13285326#comment-13285326
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Kang Xiao commented on HADOOP-7030:
-----------------------------------

tow question about the patch 

1.If new rack and host added to the cluster, it will resolve rack name to 
DEFAULT_RACK. It maybe better to allow reload of the config file.

2.The following code set initialized to be true before load(). It may cause the 
config file not fully loaded if some exception throwed by load().

{code}
+    public synchronized List<String> resolve(List<String> names) {
+      if (!initialized) {
+        initialized = true;
+        load();
+      }
{code}
                
> Add TableMapping topology implementation to read host to rack mapping from a 
> file
> ---------------------------------------------------------------------------------
>
>                 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: Tom White
>             Fix For: 2.0.0-alpha
>
>         Attachments: HADOOP-7030-2.patch, HADOOP-7030-branch-1.patch, 
> HADOOP-7030.patch, HADOOP-7030.patch, HADOOP-7030.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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