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https://issues.apache.org/jira/browse/HDFS-1351?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12901758#action_12901758
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dhruba borthakur commented on HDFS-1351:
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In particular, the following interface in BlockPlacementPolicy.java could
return null:
{code}
abstract public DatanodeDescriptor chooseReplicaToDelete(FSInodeInfo srcInode,
Block block,
short replicationFactor,
Collection<DatanodeDescriptor>
existingReplicas,
Collection<DatanodeDescriptor>
moreExistingReplicas);
{code}
> Make it possible for BlockPlacementPolicy to return null
> --------------------------------------------------------
>
> Key: HDFS-1351
> URL: https://issues.apache.org/jira/browse/HDFS-1351
> Project: Hadoop HDFS
> Issue Type: Test
> Components: name-node
> Affects Versions: 0.22.0
> Reporter: Dmytro Molkov
> Assignee: Dmytro Molkov
>
> The idea is to modify FSNamesystem.chooseExcessReplicates code, so it can
> accept a null return from chooseReplicaToDelete which will indicate that
> NameNode should not be deleting extra replicas.
> One possible usecase - if there are nodes being added to the cluster that
> might have corrupt replicas on them you do not want to delete other replicas
> until the block scanner finished scanning every block on the datanode.
> This will require additional work on the implementation of the
> BlockPlacementPolicy, but with this JIRA I just wanted to create a basis for
> future improvements.
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