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https://issues.apache.org/jira/browse/HDFS-11790?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16003869#comment-16003869
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Manoj Govindassamy commented on HDFS-11790:
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[~mingma],
Please take a look at the problem description and let us know your thoughts.
I think {{BlockManager#computeReconstructionWorkForBlocks()}} and
{{BlockManager#validateReconstructionWork()}} should be aware of IN_MAINT DNs
and avoid chosing them as source datanodes for re-replication.
> Decommissioning of a DataNode after MaintenanceState takes a very long time
> to complete
> ---------------------------------------------------------------------------------------
>
> Key: HDFS-11790
> URL: https://issues.apache.org/jira/browse/HDFS-11790
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: hdfs
> Affects Versions: 3.0.0-alpha1
> Reporter: Manoj Govindassamy
> Assignee: Manoj Govindassamy
>
> *Problem:*
> When a DataNode is requested for Decommissioning after it successfully
> transitioned to MaintenanceState (HDFS-7877), the decommissioning state
> transition is stuck for a long time even for very small number of blocks in
> the cluster.
> *Details:*
> * A DataNode DN1 wa requested for MaintenanceState and it successfully
> transitioned from ENTERING_MAINTENANCE state IN_MAINTENANCE state as there
> are sufficient replication for all its blocks.
> * As DN1 was in maintenance state now, the DataNode process was stopped on
> DN1. Later the same DN1 was requested for Decommissioning.
> * As part of Decommissioning, all the blocks residing in DN1 were requested
> for re-replicated to other DataNodes, so that DN1 could transition from
> ENTERING_DECOMMISSION to DECOMMISSIONED.
> * But, re-replication for few blocks was stuck for a long time. Eventually it
> got completed.
> * Digging the code and logs, found that the IN_MAINTENANCE DN1 was chosen as
> a source datanode for re-replication of few of the blocks. Since DataNode
> process on DN1 was already stopped, the re-replication was stuck for a long
> time.
> * Eventually PendingReplicationMonitor timed out, and those re-replication
> were re-scheduled for those timed out blocks. Again, during the
> re-replication also, the IN_MAINT DN1 was chose as a source datanode for few
> of the blocks leading to timeout again. This iteration continued for few
> times until all blocks get re-replicated.
> * By design, IN_MAINT datandoes should not be chosen for any read or write
> operations.
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