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Message-ID: <13592826.9831275941466920.JavaMail.jira@thor>
Date: Mon, 7 Jun 2010 16:11:06 -0400 (EDT)
From: "Hairong Kuang (JIRA)" <jira@apache.org>
To: hdfs-issues@hadoop.apache.org
Subject: [jira] Commented: (HDFS-1057) Concurrent readers hit
 ChecksumExceptions if following a writer to very end of file
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    [ https://issues.apache.org/jira/browse/HDFS-1057?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12876389#action_12876389 ] 

Hairong Kuang commented on HDFS-1057:
-------------------------------------

The append design document discussed this scenario, in which it says it is OK to throw an exception because the chance of hitting this is low. But the semantics you made in 0.20 seems fine to me too.

> 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: 0.21.0, 0.22.0, 0.20-append
>            Reporter: Todd Lipcon
>            Assignee: sam rash
>            Priority: Blocker
>         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
>
>
> 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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