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From "Liyin Tang (Created) (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HBASE-5259) Normalize the RegionLocation in TableInputFormat by the reverse DNS lookup.
Date Mon, 23 Jan 2012 18:38:40 GMT
Normalize the RegionLocation in TableInputFormat by the reverse DNS lookup.

                 Key: HBASE-5259
                 URL: https://issues.apache.org/jira/browse/HBASE-5259
             Project: HBase
          Issue Type: Improvement
            Reporter: Liyin Tang
            Assignee: Liyin Tang

Assuming the HBase and MapReduce running in the same cluster, the TableInputFormat is to override
the split function which divides all the regions from one particular table into a series of
mapper tasks. So each mapper task can process a region or one part of a region. Ideally, the
mapper task should run on the same machine on which the region server hosts the corresponding
region. That's the motivation that the TableInputFormat sets the RegionLocation so that the
MapReduce framework can respect the node locality. 

The code simply set the host name of the region server as the HRegionLocation. However, the
host name of the region server may have different format with the host name of the task tracker
(Mapper task). The task tracker always gets its hostname by the reverse DNS lookup. And the
DNS service may return different host name format. For example, the host name of the region
server is correctly set as a.b.c.d while the reverse DNS lookup may return a.b.c.d. (With
an additional doc in the end).

So the solution is to set the RegionLocation by the reverse DNS lookup as well. No matter
what host name format the DNS system is using, the TableInputFormat has the responsibility
to keep the consistent host name format with the MapReduce framework.

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