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https://issues.apache.org/jira/browse/HDFS-1057?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12875276#action_12875276
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Hairong Kuang commented on HDFS-1057:
-------------------------------------
Thank Sam for working on the patch for trunk. Here are my comments:
# BlockSender.java:
#* the condition replica.getBytesOnDisk() < replicaVisibleLength should be
gtBytesOnDisk() < startOffset + length. This guarantees that the bytes to be
read have already flushed to the disk.
#* When the while loop exits and the bytes still have not flushed to disk yet,
BlockSender should throw an IOException.
#* It seems to me that we should remove the use of replicaVisisbleLength from
BlockSender;
#* the way to calculate endOffset should be
{code}
if (startOffset + length falls into the same chunk where
chunkChecksum.getDataLength() is located {
endOffset = chunkChecksum.getDataLength(); --- case 1
} else {
endOffset = chunk boundary where (startOffset + length) is located
}
{code}
#* In case 1, the last chunk's checksum does not need to be read from disk.
# ReplicaInPipeline, ReplicaPipeInterface, and ReplicaBeingWritten
#* I do not think we need to make any change to ReplicaInPipeline and
ReplicaPipeInterface
#* We just need to adds the attribute lastChecksum and two synchronized method
to ReplicaBeingWritten. Would it be more readable if we use the method names as
getLastChecksumAndDataLen and setLastChecksumAndDataLen.
> 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
>
>
> 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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