[jira] [Commented] (HDFS-15634) Invalidate block on decommissioning DataNode after replication

["Adam Binford (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HDFS-15634?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17844437#comment-17844437 ] 

Adam Binford commented on HDFS-15634:
-------------------------------------

Chiming in on a 4 year old issue, we've hit similar issues where returning a node after decommissioning it cause the active namenode to failover because it holds the write lock too long processing the redundant blocks. In our case we have around ~120k blocks on a single data node across three drives. I assume `DatanodeStorageInfo` represents a single drive? In which case the write lock is only released after processing all blocks on a single drive.

> Invalidate block on decommissioning DataNode after replication
> --------------------------------------------------------------
>
>                 Key: HDFS-15634
>                 URL: https://issues.apache.org/jira/browse/HDFS-15634
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: hdfs
>            Reporter: Fengnan Li
>            Assignee: Fengnan Li
>            Priority: Major
>              Labels: pull-request-available
>         Attachments: write lock.png
>
>          Time Spent: 1h
>  Remaining Estimate: 0h
>
> Right now when a DataNode starts decommission, Namenode will mark it as decommissioning and its blocks will be replicated over to different DataNodes, then marked as decommissioned. These blocks are not touched since they are not counted as live replicas.
> Proposal: Invalidate these blocks once they are replicated and there are enough live replicas in the cluster.
> Reason: A recent shutdown of decommissioned datanodes to finished the flow caused Namenode latency spike since namenode needs to remove all of the blocks from its memory and this step requires holding write lock. If we have gradually invalidated these blocks the deletion will be much easier and faster.



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