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From Chris Nauroth <cnaur...@hortonworks.com>
Subject Re: Hadoop/HDFS/POSIX
Date Fri, 03 Jun 2016 20:02:17 GMT
Unfortunately, I'm not aware of any comprehensive documentation on how HDFS adheres to POSIX
and how it differs.  To some degree, it's possible to look at the FileSystem specification
and corresponding contract tests as a source of information, but it's not structured to answer
that question directly.  I filed HADOOP-13104 to track improving that, but I haven't been
able to work on it yet.



There is also some discussion of POSIX specifically related to permission handling in the
HDFS permissions guide.


--Chris Nauroth

From: Gagan Brahmi <gaganbrahmi@gmail.com<mailto:gaganbrahmi@gmail.com>>
Date: Friday, June 3, 2016 at 9:18 AM
To: Deepak Goel <deicool@gmail.com<mailto:deicool@gmail.com>>
Cc: user <user@hadoop.apache.org<mailto:user@hadoop.apache.org>>
Subject: Re: Hadoop/HDFS/POSIX

AFAIK the major difference include the simplified Coherency model<https://hadoop.apache.org/docs/r2.7.1/hadoop-project-dist/hadoop-hdfs/HdfsDesign.html#Simple_Coherency_Model>
in HDFS.

The other one is the file permissions. The read (r), write (w) & execute (x) works the
same way for directories in HDFS like a POSIX file system. But for the  files, execute permission
is ignored in HDFS since you can't really execute a file in HDFS.


Gagan Brahmi

On Fri, Jun 3, 2016 at 1:30 AM, Deepak Goel <deicool@gmail.com<mailto:deicool@gmail.com>>


Namaskara~Nalama~Guten Tag~Bonjour

The Hadoop document gives a pointer that HDFS relaxes some POSIX requirements to maintain
high throughput rate.


But it does not give exactly what are the things which it relaxes? Any idea which programs
should I look into to find the things which HDFS relaxes?


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