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From Dhruba Borthakur <dhr...@gmail.com>
Subject Re: Question regarding HDFS Recovery
Date Wed, 20 May 2009 17:24:37 GMT
The NN has a timer for dead-clients. When the HARD_LIMIT (1 hour) expires,
the NN extracts the primary datanode from the
INodeFileUnderConstruction.targets and asks the primary datanode to recover
the lease. At the end of the lease recovery, the primary datanode invokes
NameNode.commitBlockSynchronisation method, and the lease recovery is
complete.

hope this helps,
thanks,
dhruba



On Wed, May 20, 2009 at 9:14 AM, Sangmin Lee <sangmin.dev@gmail.com> wrote:

> I am looking at 0.19.0(or maybe 0.19.1) and 0.20.0.
> In fact, I am still curious about the case (maybe too much extream case)
> where
> a client open a file, request a block and prematurely dies.
> Also all datanodes go dead.
> I don't see how the lease will be recovered or reaped in this case.
> Don't we need some mechanism that discards the block and removes the lease
> after several attempts for lease recovery ?
>
> Thanks,
> Sangmin
>
> On Wed, May 20, 2009 at 10:40 AM, Edward J. Yoon <edwardyoon@apache.org
> >wrote:
>
> > Can I ask what version do you read? You looks reach so deeply into the
> > architecture of a system...
> >
> > On Thu, May 21, 2009 at 12:28 AM, Sangmin Lee <sangmin.dev@gmail.com>
> > wrote:
> > > Okay.. I was going dumb by misreading some source code.
> > > Please ignore my question regarding this.
> > > Sorry about this.
> > >
> > > Sangmin
> > >
> > > On Tue, May 19, 2009 at 11:59 PM, Sangmin Lee <sangmin.dev@gmail.com>
> > wrote:
> > >
> > >> Hi all,
> > >>
> > >> I have some question regarding the hdfs recovery mechanism.
> > >>
> > >> I see that INodeFileUnderConstruction has a "targets" field that
> stores
> > >> list of datanodes which store its last block.
> > >> However, I don't see them being used at all except that
> > >> "internalReleaseLease" function uses the length of the datanode list.
> > >> Is there any other use of the "target" fields rather than checking its
> > >> length?
> > >>
> > >> Could anyone shed some light on this?
> > >>
> > >> Thanks,
> > >> Sangmin
> > >>
> > >
> >
> >
> >
> > --
> > Best Regards, Edward J. Yoon @ NHN, corp.
> > edwardyoon@apache.org
> > http://blog.udanax.org
> >
>

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