[jira] Commented: (HDFS-778) DistributedFileSystem.getFileBlockLocations() may occasionally return numeric ips as hostnames.

["Suresh Srinivas (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HDFS-778?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12780386#action_12780386 ] 

Suresh Srinivas commented on HDFS-778:
--------------------------------------

Looks like datanodes are registering with IP address as the name in registration instead of host name. I in suspect o.a.h.net.DNS, {{InetAddress.getLocalHost().getCanonicalHostName()}} is returning the IP address. Not sure if this is due to some java SecurityManager issue.

> DistributedFileSystem.getFileBlockLocations() may occasionally return numeric ips as hostnames.
> -----------------------------------------------------------------------------------------------
>
>                 Key: HDFS-778
>                 URL: https://issues.apache.org/jira/browse/HDFS-778
>             Project: Hadoop HDFS
>          Issue Type: Bug
>            Reporter: Hong Tang
>
> DistributedFileSystem.getFileBlockLocations() may occasionally return numeric ips as hostnames. This seems to be a breach of the FileSystem.getFileBlockLocation() contract:
> {noformat}
>   /**
>    * Return an array containing hostnames, offset and size of 
>    * portions of the given file.  For a nonexistent 
>    * file or regions, null will be returned.
>    *
>    * This call is most helpful with DFS, where it returns 
>    * hostnames of machines that contain the given file.
>    *
>    * The FileSystem will simply return an elt containing 'localhost'.
>    */
>   public BlockLocation[] getFileBlockLocations(FileStatus file, 
>       long start, long len) throws IOException
> {noformat}
> One (maybe minor) consequence of this issue is: When a job includes such numeric ips in in its splits' locations, JobTracker would not be able to assign the job's map tasks local to the file blocks.
> We should either fix the implementation or change the contract. In the latter case, JobTracker needs to be fixed to maintain both the hostnames and ips of the TaskTrackers.

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