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From "sam rash (JIRA)" <j...@apache.org>
Subject [jira] Updated: (HDFS-1057) Concurrent readers hit ChecksumExceptions if following a writer to very end of file
Date Fri, 25 Jun 2010 18:47:52 GMT

     [ https://issues.apache.org/jira/browse/HDFS-1057?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

sam rash updated HDFS-1057:
---------------------------

    Attachment: hdfs-1057-trunk-5.txt

-returns 0 length only if all DNs are missing the replica (any other io exception will cause
client to get exception and it can retry)
-my diff viewer does not show any whitespace or indentation changes, but please advise if
you see any 

> 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-1057-0.20-append.patch, 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
>
>
> 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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