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From Hairong Kuang <hair...@yahoo-inc.com>
Subject Re: Query over DFSClient
Date Wed, 31 Mar 2010 17:33:49 GMT
> However, I couldn't figure out where this exception is thrown.
After lastException is set, the exception is thrown when next
FSOutputStream.write or close is called.

Hairong

On 3/31/10 6:01 AM, "Ankur C. Goel" <gankur@yahoo-inc.com> wrote:

> Pallavi,
>              If a DFSClient is not able to write a block to any of the
> datanodes given by namenode it retries N times before aborting.
> See - https://issues.apache.org/jira/browse/HDFS-167
> This should be handled by the application as this indicates that something is
> seriously wrong with your cluster
> 
> Hope this helps
> -@nkur
> 
> On 3/31/10 4:59 PM, "Pallavi Palleti" <pallavi.palleti@corp.aol.com> wrote:
> 
> Hi,
> 
> I am looking into hadoop-20 source code for below issue. From DFSClient,
> I could see that once the datanodes given by namenode are not reachable,
> it is setting "lastException" variable to error message saying "recovery
> from primary datanode is failed N times, aborting.."(line No:2546 in
> processDataNodeError).  However, I couldn't figure out where this
> exception is thrown. I could see the throw statement in isClosed() but
> not finding the exact sequence after Streamer exits with lastException
> set to isClosed() method call. It would be great if some one could shed
> some light on this. I am essentially looking whether DFSClient
> approaches namenode in the case of failure of all datanodes that
> namenode has given for a given data block previously.
> 
> Thanks
> Pallavi
> 
> 
> On 03/30/2010 05:01 PM, Pallavi Palleti wrote:
>> Hi,
>> 
>> Could some one kindly let me know if the DFSClient takes care of
>> datanode failures and attempt to write to another datanode if primary
>> datanode (and replicated datanodes) fail. I looked into the souce code
>> of DFSClient and figured out that it attempts to write to one of the
>> datanodes in pipeline and fails if it failed to write to at least one
>> of them. However, I am not sure as I haven't explored fully. If so, is
>> there a way of querying namenode to provide different datanodes in the
>> case of failure. I am sure the Mapper would be doing similar
>> thing(attempting to fetch different datanode from namenode)  if it
>> fails to write to datanodes. Kindly let me know.
>> 
>> Thanks
>> Pallavi
>> 
> 


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