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https://issues.apache.org/jira/browse/HDFS-15160?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17120455#comment-17120455
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Jiang Xin edited comment on HDFS-15160 at 6/2/20, 9:25 AM:
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Hi [~sodonnell] ,
Thanks for your quick reply.
I have one more question, is it safe to change
FsDatasetImpl#getBlockLocalPathInfo and
DataNode#transferReplicaForPipelineRecovery to read lock?As you mentioned
above, both of them would change generationStamp, the `synchronized(replica) `
in FsDatasetImpl#getBlockLocalPathInfo seems not protected generationStamp from
being changed in other methods. Would you like to have a double check?
Besides, FsDatasetImpl#getBlockReports could be changed to read lock in my
opinion, What do you think？
Thanks.
was (Author: jiang xin):
Hi [~sodonnell] ,
Thanks for your quick reply. I have one more question, is it safe to change
FsDatasetImpl#getBlockLocalPathInfo and
DataNode#transferReplicaForPipelineRecovery to read lock?
As you mentioned above, both of them would change generationStamp, the
`synchronized(replica) ` in FsDatasetImpl#getBlockLocalPathInfo seems not
protected generationStamp from being changed in other methods. Would you like
to have a review?
Thanks.
> ReplicaMap, Disk Balancer, Directory Scanner and various FsDatasetImpl
> methods should use datanode readlock
> -----------------------------------------------------------------------------------------------------------
>
> Key: HDFS-15160
> URL: https://issues.apache.org/jira/browse/HDFS-15160
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: datanode
> Affects Versions: 3.3.0
> Reporter: Stephen O'Donnell
> Assignee: Stephen O'Donnell
> Priority: Major
> Attachments: HDFS-15160.001.patch, HDFS-15160.002.patch,
> HDFS-15160.003.patch, HDFS-15160.004.patch, HDFS-15160.005.patch,
> HDFS-15160.006.patch, image-2020-04-10-17-18-08-128.png,
> image-2020-04-10-17-18-55-938.png
>
>
> Now we have HDFS-15150, we can start to move some DN operations to use the
> read lock rather than the write lock to improve concurrence. The first step
> is to make the changes to ReplicaMap, as many other methods make calls to it.
> This Jira switches read operations against the volume map to use the readLock
> rather than the write lock.
> Additionally, some methods make a call to replicaMap.replicas() (eg
> getBlockReports, getFinalizedBlocks, deepCopyReplica) and only use the result
> in a read only fashion, so they can also be switched to using a readLock.
> Next is the directory scanner and disk balancer, which only require a read
> lock.
> Finally (for this Jira) are various "low hanging fruit" items in BlockSender
> and fsdatasetImpl where is it fairly obvious they only need a read lock.
> For now, I have avoided changing anything which looks too risky, as I think
> its better to do any larger refactoring or risky changes each in their own
> Jira.
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