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From "Uma Maheswara Rao G (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-3421) ( Dynamic Rack Addition ) : After adding new Datanode in cluster not possible to change the rack of Datanode without restarts the Namenode.
Date Mon, 28 May 2012 11:16:23 GMT

    [ https://issues.apache.org/jira/browse/HDFS-3421?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13284370#comment-13284370
] 

Uma Maheswara Rao G commented on HDFS-3421:
-------------------------------------------

Looks it is caching the mapping because you might use CachedDNSToSwitchMapping#resolve internally
for resolving .

Here is the relevent code, where it caches the mappings

{code}
@Override
  public List<String> resolve(List<String> names) {
    // normalize all input names to be in the form of IP addresses
    names = NetUtils.normalizeHostNames(names);

    List <String> result = new ArrayList<String>(names.size());
    if (names.isEmpty()) {
      return result;
    }

    List<String> uncachedHosts = getUncachedHosts(names);

    // Resolve the uncached hosts
    List<String> resolvedHosts = rawMapping.resolve(uncachedHosts);
    //cache them
    cacheResolvedHosts(uncachedHosts, resolvedHosts);
    //now look up the entire list in the cache
    return getCachedHosts(names);

  }
{code}

I am not sure, wehtehr we have an option to disable this caching by using other mappings.
Any one know about that?
                
> ( Dynamic Rack Addition ) : After adding new Datanode in cluster not possible to change
the rack of Datanode without restarts the Namenode.
> -------------------------------------------------------------------------------------------------------------------------------------------
>
>                 Key: HDFS-3421
>                 URL: https://issues.apache.org/jira/browse/HDFS-3421
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: name-node
>         Environment: One NameNode and three DataNodes each datanode in diffrent rack
>            Reporter: surendra singh lilhore
>
> Scenario: 
> I am using the script Mapping Technique for Dynamic Addition of rack.
> 1. Namenode is running with three datanode(xx.xx.xx.45,xx.xx.xx.91,xx.xx.xx.157)
> xx.xx.xx.45 : /datacenter1/rack1
> xx.xx.xx.91 : /datacenter1/rack2
> xx.xx.xx.157 :/datacenter1/rack3
> 2. Stop datanode xx.xx.xx.157.
> 3. change the rack of xx.xx.xx.157 to rack4 in Script file.
> 'xx.xx.xx.45' : '/datacenter1/rack1'
> 'xx.xx.xx.91' : '/datacenter1/rack2'
> 'xx.xx.xx.157' : '/datacenter1/rack4'
> 4. Start datanode xx.xx.xx.157.
> Expected Result : Datanode Should be add in rack4
> Actual Result :   Datanode Added in old rack only (rack3).

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