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From "Todd Lipcon (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HDFS-1057) Concurrent readers hit ChecksumExceptions if following a writer to very end of file
Date Tue, 04 May 2010 23:38:05 GMT

    [ https://issues.apache.org/jira/browse/HDFS-1057?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12864072#action_12864072
] 

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

That sounds fine - I was making those comments so you could incorporate them into the trunk
patch when you get there.

I am still curious about whether you verified that transferTo still works (either via benchmark
or instrumentation/strace)

> 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
>            Assignee: sam rash
>            Priority: Blocker
>         Attachments: conurrent-reader-patch-1.txt, conurrent-reader-patch-2.txt, conurrent-reader-patch-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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