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https://issues.apache.org/jira/browse/HDFS-1057?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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sam rash updated HDFS-1057:
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    Attachment: hdfs-1057-trunk-4.txt

includes requested changes by hairong.  also handles immediate reading of new 
files by translating a ReplicaNotFoundException into a 0-length block within 
DFSInputStream for under construction files

> Concurrent readers hit ChecksumExceptions if following a writer to very end 
> of file
> -----------------------------------------------------------------------------------
>
>                 Key: HDFS-1057
>                 URL: https://issues.apache.org/jira/browse/HDFS-1057
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>          Components: data-node
>    Affects Versions: 0.20-append, 0.21.0, 0.22.0
>            Reporter: Todd Lipcon
>            Assignee: sam rash
>            Priority: Blocker
>             Fix For: 0.20-append
>
>         Attachments: conurrent-reader-patch-1.txt, 
> conurrent-reader-patch-2.txt, conurrent-reader-patch-3.txt, 
> hdfs-1057-trunk-1.txt, hdfs-1057-trunk-2.txt, hdfs-1057-trunk-3.txt, 
> hdfs-1057-trunk-4.txt
>
>
> In BlockReceiver.receivePacket, it calls replicaInfo.setBytesOnDisk before 
> calling flush(). Therefore, if there is a concurrent reader, it's possible to 
> race here - the reader will see the new length while those bytes are still in 
> the buffers of BlockReceiver. Thus the client will potentially see checksum 
> errors or EOFs. Additionally, the last checksum chunk of the file is made 
> accessible to readers even though it is not stable.

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