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Posted to common-issues@hadoop.apache.org by "Haryadi Gunawi (JIRA)" <ji...@apache.org> on 2012/09/18 19:20:07 UTC
[jira] [Updated] (HADOOP-923) DFS Scalability: datanode heartbeat
timeouts cause cascading timeouts of other datanodes
[ https://issues.apache.org/jira/browse/HADOOP-923?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Haryadi Gunawi updated HADOOP-923:
----------------------------------
Description:
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.
was:
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.
> 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 Common
> Issue Type: Bug
> Affects Versions: 0.10.1
> Reporter: dhruba borthakur
> Assignee: 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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