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https://issues.apache.org/jira/browse/HDFS-15160?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17065332#comment-17065332
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Wei-Chiu Chuang commented on HDFS-15160:
----------------------------------------
Looks correct to me.
nit:
{code}
/**
* Acquire the lock of the data set.
*/
AutoCloseableLock acquireDatasetLock();
/***
* Acquire the read lock of the data set.
* @return The AutoClosable read lock instance.
*/
AutoCloseableLock acquireDatasetReadLock();
{code}
It would be great to make the javadoc more clear of the expected behavior. With
the read lock, it is expected that the block map does it change; however, the
Block data structure may be updated (update gen stamp, etc). Am I correct?
> 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
>
>
> 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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