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https://issues.apache.org/jira/browse/HDFS-1605?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14535173#comment-14535173
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Ravi Prakash commented on HDFS-1605:
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Thanks for the patch [~kartheek]
I'm afraid we may have changed the synchronization model for DFSInputStream in
this patch. For example, earlier 2 threads: one accessing getCurrentDatanode()
and another seekToNewSource() ; would have synchronized on a single lock.
However now, the two threads could proceed at the same time and hence there's a
race condition on currentNode. Is my understanding correct?
> Convert DFSInputStream synchronized sections to a ReadWrite lock
> ----------------------------------------------------------------
>
> Key: HDFS-1605
> URL: https://issues.apache.org/jira/browse/HDFS-1605
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: hdfs-client
> Reporter: dhruba borthakur
> Assignee: dhruba borthakur
> Labels: BB2015-05-RFC
> Attachments: DFSClientRWlock.1.txt, DFSClientRWlock.3.txt,
> HADOOP-1605-trunk.patch, HDFS-1605.txt
>
>
> Hbase does concurrent preads from multiple threads to different blocks of the
> same hdfs file. Each of these pread calls invoke
> DFSInputStream.getFileLength() and DFSInputStream.getBlockAt(). These methods
> are "synchronized", thus causing all the concurrent threads to serialize. It
> would help performance to convert this to a Read/Write lock
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