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From "Thanh Do (JIRA)" <j...@apache.org>
Subject [jira] Reopened: (HDFS-1384) NameNode should give client the first node in the pipeline from different rack other than that of excludedNodes list in the same rack.
Date Sun, 12 Sep 2010 01:00:33 GMT

     [ https://issues.apache.org/jira/browse/HDFS-1384?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Thanh Do reopened HDFS-1384:
----------------------------


Dhruba,

I think I make a bad description of the bug.
The excludedList does the job.
But in this case, the excludedList contains only nodes from rack 0,
and when client retries, NN give it the first dn in the pipe which is
also in rack 0 too. Hence when client tries to create the pipe,
it contacts the first dn and fails (because of network partition).
So the problem here is that NN keeps giving client node that 
from the same rack (in this case, i.e rack 0). And because
client cannot see any node in rack 0, it retries 5 times and fail.

> NameNode should give client the first node in the pipeline from different rack  other
than that of excludedNodes list in the same rack.
> ---------------------------------------------------------------------------------------------------------------------------------------
>
>                 Key: HDFS-1384
>                 URL: https://issues.apache.org/jira/browse/HDFS-1384
>             Project: Hadoop HDFS
>          Issue Type: Bug
>    Affects Versions: 0.20-append, 0.20.1
>            Reporter: Thanh Do
>
> We saw a case that NN keeps giving client nodes from the same rack, hence an exception

> from client when try to setup the pipeline. Client retries 5 times and fails.
>  
> Here is more details. Support we have 2 rack
> - Rack 0: from dn1 to dn7
> - Rack 1: from dn8 to dn14
> Client asks for 3 dns and NN replies with dn1, dn8 and dn9, for example.
> Because there is network partition, so client doesn't see any node in Rack 0.
> Hence, client add dn1 to excludedNodes list, and ask NN again.
> Interestingly, NN picks a different node (from those in excludedNodes) in Rack 0, 
> and gives back to client, and so on. Client keeps retrying and after 5 times of retrials,

> write fails.
> This bug was found by our Failure Testing Service framework:
> http://www.eecs.berkeley.edu/Pubs/TechRpts/2010/EECS-2010-98.html
> For questions, please email us: Thanh Do (thanhdo@cs.wisc.edu) and 
> Haryadi Gunawi (haryadi@eecs.berkeley.edu)

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