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From Dhruba Borthakur <dhr...@gmail.com>
Subject Re: Intelligence of decommission
Date Fri, 28 Aug 2009 20:41:24 GMT
when a user issues the decommission command, all the blocks that are
currently residing on it are inserted into the to-be-replicated queue. Then
the ReplicationMonitor inside the namenode starts replicating these blocks
(during this period, the replica on the machine being decommissioned is used
for reads, but is not considered a valid replica by the ReplicationMonitor).

hope this helps,

On Fri, Aug 28, 2009 at 1:07 PM, Allen Wittenauer

> Hi.
> As I sit here and wait for node decommission to finish, I was wondering
> about the intelligence of the decision making.  [The name nodes, not mine.
> :) ]
> Let's say I have the following scenario:
> I have two files.  Both files consist of one block with a replication
> factor
> of three.  I decommission two nodes.  File #1 has two of its replicas on
> the
> two nodes I am decommissioning.  File #2 has only one of its replicas on
> one
> of the two nodes I am decommissioning.
> Is the block with two replicas on the two nodes I am decommissioning given
> priority?  How does the name node decide which blocks to re-replicate
> first?
> Thanks.

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