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https://issues.apache.org/jira/browse/HADOOP-985?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12471046
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Raghu Angadi commented on HADOOP-985:
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I was thinking of thread local as well.. but was not sure if it was normal
practice or not. will do that.
Regd hostname, should we just let Datanode behave pretty much how it does now
and not bother resolving it Namenode?
> Namenode should identify DataNodes as ip:port instead of hostname:port
> ----------------------------------------------------------------------
>
> Key: HADOOP-985
> URL: https://issues.apache.org/jira/browse/HADOOP-985
> Project: Hadoop
> Issue Type: Improvement
> Components: dfs
> Affects Versions: 0.11.0
> Reporter: Raghu Angadi
> Assigned To: Raghu Angadi
> Fix For: 0.12.0
>
>
> 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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