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From "Tsz Wo (Nicholas), SZE (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-1057) Concurrent readers hit ChecksumExceptions if following a writer to very end of file
Date Thu, 19 May 2011 22:15:47 GMT

    [ https://issues.apache.org/jira/browse/HDFS-1057?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13036530#comment-13036530
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Tsz Wo (Nicholas), SZE commented on HDFS-1057:
----------------------------------------------

Todd, well done!  Thanks for investigating it.

> 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, 0.21.0, 0.22.0
>
>         Attachments: HDFS-1057-0.20-append.patch, 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, hdfs-1057-trunk-5.txt, hdfs-1057-trunk-6.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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