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From "sam rash (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-1057) Concurrent readers hit ChecksumExceptions if following a writer to very end of file
Date Wed, 18 May 2011 23:24:48 GMT

    [ https://issues.apache.org/jira/browse/HDFS-1057?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13035851#comment-13035851
] 

sam rash commented on HDFS-1057:
--------------------------------

the last time I debugged the test failure, it exposed a socket/fd leak in a completely unrelated
part of the code.  The test failing here also has 0 to do with the added feature--because
it closes/opens files in rapid succession, it is prone expose resource leaks.

Removing this test (or feature) won't take away the underlying problem that should be looked
at.

> 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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