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Date: Fri, 27 Jan 2012 06:23:56 +0000 (UTC)
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Subject: [jira] [Commented] (HBASE-5259) Normalize the RegionLocation in
 TableInputFormat by the reverse DNS lookup.
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    [ https://issues.apache.org/jira/browse/HBASE-5259?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13194512#comment-13194512 ] 

Phabricator commented on HBASE-5259:
------------------------------------

gqchen has commented on the revision "[jira][HBASE-5259] Normalize the RegionLocation in TableInputFormat by the reverse DNS lookup.".

INLINE COMMENTS
  src/main/java/org/apache/hadoop/hbase/mapreduce/TableInputFormatBase.java:89 I guess this is more like a personal preference. For non-trivial data structures, I personally find it helpful to have the type in the variable name, so that when you read the code where the variable is being used, you don't have to guess.

REVISION DETAIL
  https://reviews.facebook.net/D1413

                
> 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
>         Attachments: D1413.1.patch, D1413.1.patch, D1413.1.patch, D1413.1.patch, D1413.2.patch, D1413.2.patch, D1413.2.patch, D1413.2.patch, D1413.3.patch, D1413.3.patch, D1413.3.patch, D1413.3.patch
>
>
> 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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