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From "Phabricator (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-5259) Normalize the RegionLocation in TableInputFormat by the reverse DNS lookup.
Date Fri, 27 Jan 2012 05:43:51 GMT

    [ https://issues.apache.org/jira/browse/HBASE-5259?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13194489#comment-13194489

Phabricator commented on HBASE-5259:

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

  src/main/java/org/apache/hadoop/hbase/mapreduce/TableInputFormatBase.java:89 Map is reflected
in the type of this field.
  My suggestion was only for your reference.
  src/main/java/org/apache/hadoop/hbase/mapreduce/TableInputFormatBase.java:198 If NamingException
is thrown out of line 201, line 202 would be skipped.
  Line 169 might be executed multiple times because regionServerAddress across multiple iterations
may carry the same (unresolvable) value.

  Correct me if I am wrong.


> 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,
> 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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