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From "Raghu Angadi (JIRA)" <j...@apache.org>
Subject [jira] Created: (HADOOP-985) Namenode should identify DataNodes as ip:port instead of hostname:port
Date Tue, 06 Feb 2007 21:26:05 GMT
Namenode should identify DataNodes as ip:port instead of hostname:port
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                 Key: HADOOP-985
                 URL: https://issues.apache.org/jira/browse/HADOOP-985
             Project: Hadoop
          Issue Type: Improvement
            Reporter: Raghu Angadi



Right now NameNode keeps track of DataNodes with "hostname:port". One proposal is to keep
track of datanodes with "ip:port". There are various concerns expressed regd hostnames and
ip. Please add your experiences here so that we have better idea on what we should fix etc.

How should be calculate datanode ip: 

            1) Just like how we calculate hostname currently with "dfs.datanode.dns.interface"
and "dfs.datanode.dns.nameserver". So if interface specified wrong, it could report ip like
127.0.0.1 which might or might not be intended.

            2) Namenode can use the remove socket address when the datanode registers. Not
sure how easy it to get this address in RPC or if this is desirable.

            3) Namenode could just resolve the hostname when a datanode registers. It could
print of a warning if the resolved ip and reported ip don't match.

One advantage of using IPs is that DFSClient does not need to resolve them when it connects
to datanode. This could save few milliseconds for each block. Also, DFSClient should check
all its ips to see if a given ip is local or not.

As far I see namenode does not resolve any DNS in normal operations since it does not actively
contact datanodes. In that sense not sure if this have any change in Namenode performance.

Thoughts?



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