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https://issues.apache.org/jira/browse/HDFS-1057?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12871285#action_12871285
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sam rash commented on HDFS-1057:
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@hairong:
I'm looking a little at implementing this in trunk (reading your append/hflush
doc from hdfs-265), and I have a question. From above:
"In each ReplcaBeingWritten, we could have two more fields to keep track of
the last consistent state: replica length and the last chunk's crc"
why does there need to be another length field? the getVisibleLenght() ==
acked bytes isn't sufficient? if the crc stored in the RBW is for that length,
you only need the additional byte[] field which is the last chunk's crc I think.
ReplicaBeingWritten.setBytesAcked() could take the crc and atomically set the
len + bytes
> 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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