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From "Alejandro Fernandez" <afernan...@hortonworks.com>
Subject Re: Review Request 31878: CopyFromLocal failed to copy Tez tarball to HDFS failed because multiple processes tried to copy to the same destination simultaneously
Date Tue, 10 Mar 2015 19:05:49 GMT


> On March 10, 2015, 6:42 p.m., Andrew Onischuk wrote:
> > Alejandro, this will make our deploy longer much, since those fs commands take lot
of time on loaded cluster.
> > 
> > Can we like set x retries with y delay for CopyFromLocal, in that case we won't
increase time of successful deployment.
> 
> Andrew Onischuk wrote:
>     Meaning this will increase time of every CopyFromLocal x2 or so, and we have a lot
of that things called, and they seems to take a lot of time even now.

What triggers this is YARN History Server START, Hive Sever 2 START, Pig Service Check, and
Spark History Server START. This also includes starting after a Rolling Upgrade.
In all of these cases, we first check if the file is already present in HDFS, so the only
performance impact comes from the actual copy the first time.
I used this approach because it guarantees 100% success. I already wrote a retry-decorator,
so I'll see what it takes to make it do a random sleep, but this will require more logic.


- Alejandro


-----------------------------------------------------------
This is an automatically generated e-mail. To reply, visit:
https://reviews.apache.org/r/31878/#review75927
-----------------------------------------------------------


On March 10, 2015, 1:41 a.m., Alejandro Fernandez wrote:
> 
> -----------------------------------------------------------
> This is an automatically generated e-mail. To reply, visit:
> https://reviews.apache.org/r/31878/
> -----------------------------------------------------------
> 
> (Updated March 10, 2015, 1:41 a.m.)
> 
> 
> Review request for Ambari, Andrew Onischuk, Jonathan Hurley, Nate Cole, and Sid Wagle.
> 
> 
> Bugs: AMBARI-9990
>     https://issues.apache.org/jira/browse/AMBARI-9990
> 
> 
> Repository: ambari
> 
> 
> Description
> -------
> 
> 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.
> 
> 
> Diffs
> -----
> 
>   ambari-common/src/main/python/resource_management/libraries/functions/dynamic_variable_interpretation.py
00b8d70 
> 
> Diff: https://reviews.apache.org/r/31878/diff/
> 
> 
> Testing
> -------
> 
> Unit tests on builds.apache.org passed,
> https://builds.apache.org/job/Ambari-trunk-test-patch/1977/
> 
> I also deployed a cluster and verified that it was able to copy the tarballs to HDFS
when installing YARN, Hive, Pig.
> 
> [root@c6408 ~]# su - hdfs -c 'hadoop fs -ls -R /hdp/apps/2.2.2.0-2538/'
> dr-xr-xr-x   - hdfs hdfs          0 2015-03-10 00:55 /hdp/apps/2.2.2.0-2538/hive
> -r--r--r--   3 hdfs hadoop   82982575 2015-03-10 00:55 /hdp/apps/2.2.2.0-2538/hive/hive.tar.gz
> dr-xr-xr-x   - hdfs hdfs            0 2015-03-10 00:57 /hdp/apps/2.2.2.0-2538/mapreduce
> -r--r--r--   3 hdfs hadoop     105000 2015-03-10 00:57 /hdp/apps/2.2.2.0-2538/mapreduce/hadoop-streaming.jar
> -r--r--r--   3 hdfs hadoop  192699956 2015-03-09 18:15 /hdp/apps/2.2.2.0-2538/mapreduce/mapreduce.tar.gz
> dr-xr-xr-x   - hdfs hdfs            0 2015-03-10 00:56 /hdp/apps/2.2.2.0-2538/pig
> -r--r--r--   3 hdfs hadoop   97542246 2015-03-10 00:56 /hdp/apps/2.2.2.0-2538/pig/pig.tar.gz
> dr-xr-xr-x   - hdfs hdfs            0 2015-03-09 18:15 /hdp/apps/2.2.2.0-2538/tez
> -r--r--r--   3 hdfs hadoop   40656789 2015-03-09 18:15 /hdp/apps/2.2.2.0-2538/tez/tez.tar.gz
> 
> 
> Thanks,
> 
> Alejandro Fernandez
> 
>


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