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Date: Thu, 8 Apr 2010 17:55:36 +0000 (UTC)
From: "Todd Lipcon (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=12855050#action_12855050 ] 

Todd Lipcon commented on HDFS-1057:
-----------------------------------

Solution 2 should work, but we still need to add to the recovery code to recompute the last chunk checksum during rbw recovery, right? (ie a DN could crash in between flushing data and metadata)

> 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
>            Reporter: Todd Lipcon
>            Priority: Critical
>
> 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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