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https://issues.apache.org/jira/browse/HADOOP-923?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Doug Cutting updated HADOOP-923:
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Resolution: Fixed
Fix Version/s: 0.12.0
Status: Resolved (was: Patch Available)
I just committed this. Thanks, Dhruba!
> DFS Scalability: datanode heartbeat timeouts cause cascading timeouts of
> other datanodes
> ----------------------------------------------------------------------------------------
>
> Key: HADOOP-923
> URL: https://issues.apache.org/jira/browse/HADOOP-923
> Project: Hadoop
> Issue Type: Bug
> Components: dfs
> Affects Versions: 0.10.1
> Reporter: dhruba borthakur
> Assigned To: dhruba borthakur
> Fix For: 0.12.0
>
> Attachments: pendingTransferThread2.patch
>
>
> The datanode sends a heartbeat to the namenode every 3 seconds. The namenode
> processes the heartbeat and sends a list of block-to-be-replicated and
> blocks-to-be-deleted as part of the heartbeat response.
> At times when a couple of datanodes fail, the heartbeat processing on the
> namenode becomes pretty heavyweight. It acquires the global FSNamesystem
> lock, traverses the neededReplication structure, generates a list of blocks
> to be replicated and responds to the heartbeat message. Determining the list
> of blocks-to-be-replciated is pretty heavyweight, takes plenty of CPU and
> blocks processing of other heartbeats because of the global FSNamesystem lock.
> It would improve scalability a lot if heartbeat processing does not require
> the FSNamesystem lock. In fact, the pre-existing "heartbeat" lock already
> exists for this purpose.
> I propose that the Heartbeat message be separate from the "retrieve
> blocks-to-replicate and blocks-to-delete" messages. The datanode can continue
> to heartbeat once every 3 seconds while it can afford to "retrieve
> blocks-to-replicate" at a much coarser interval. Heartbeat processing on the
> namenode will be fast because it does not require the global FSNamesystem
> lock. Moreover, a datanode failure will not aggrevate the heartbeat
> processing time on the namenode.
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