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https://issues.apache.org/jira/browse/HBASE-5259?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13194926#comment-13194926
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Phabricator commented on HBASE-5259:
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tedyu 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:198
I am learning about the possibilities of reverse DNS failure:
http://www.crucialp.com/resources/tutorials/web-hosting/how-reverse-dns-works-rdns.php
I think we should be prepared for such occasion as I outlined @ 9:43pm.
Just for your reference.
src/main/java/org/apache/hadoop/hbase/mapreduce/TableInputFormatBase.java:198
bq. this error case which isn't supposed to happen
If I understand the statement correctly, you didn't say 'definitely not
possible'.
My earlier analysis w.r.t. NamingException shows that we would incur extra
delay in case reverse DNS fails since the assignment on line 169 doesn't put
the fall back value into cache.
This can be regarded as performance regression compared to previous
implementation where reverse DNS is not taken into account.
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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