[jira] [Created] (AMBARI-9990) CopyFromLocal failed to copy Tez tarball to HDFS failed because multiple processes tried to copy to the same destination simultaneously

["Alejandro Fernandez (JIRA)" <ji...@apache.org>]

Alejandro Fernandez created AMBARI-9990:
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             Summary: CopyFromLocal failed to copy Tez tarball to HDFS failed because multiple processes tried to copy to the same destination simultaneously
                 Key: AMBARI-9990
                 URL: https://issues.apache.org/jira/browse/AMBARI-9990
             Project: Ambari
          Issue Type: Bug
          Components: ambari-server
    Affects Versions: 2.0.0
            Reporter: Alejandro Fernandez
            Assignee: Alejandro Fernandez
             Fix For: 2.0.0


Pig Service Check and Hive Server 2 START ran on 2 different machines during the stack installation and failed to copy the tez tarball to HDFS.

I was able to reproduce this locally by calling CopyFromLocal from two clients simultaneously. See the HDFS audit log, datanode logs on c6408 & c6410, and namenode log on c6410.

The copyFromLocal command's behavior is:
* Try to create a temporary file <filename>._COPYING_ and write the real data there
* If hit any exception, delete the file with the name <filename>._COPYING_

Thus we have the following race condition in this test:
Process P1 created file "tez.tar.gz._COPYING_" and wrote data to it
Process P2 fired the same copyFromLocal command and hit exception because it could not get the lease
P2 then deleted the file "tez.tar.gz._COPYING_"
P1 could not close the file "tez.tar.gz._COPYING_" since it had been deleted by P2. The exception would say "could not find lease for file..."
In general we do not have the correct synchronization guarantee for the "copyFromLocal" command.

One solution is for the destination file name to be unique. Because the mv command is synchronized by the namenode, at least one of them will succeed in naming the file.



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