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Date: Tue, 22 Jun 2010 18:35:51 -0400 (EDT)
From: "sam rash (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=12881421#action_12881421 ] 

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

i have an updated patch, but it does not yet handle the missing replicas as 0 sized for under construction.  there may be other 20 patches to port to make this happen.  

> 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
>
>
> 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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