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https://issues.apache.org/jira/browse/HDFS-1057?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12875801#action_12875801
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sam rash commented on HDFS-1057:
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Thanks for the quick review.
I understand most of the comments, but have a couple of questions:
1. replicaVisibleLength was here before I made any changes. Why is it not
valid? I understood it to be an upper bound on the bytes that could be read
from this block. Is it the case that start + length <= replicaVisibleLength
and we want to optimize?
(the for loop to wait for bytes on disk >= visible length was here before, I
just moved it earlier in the constructor)
2. not sure I understand endOffset. This was again a variable that already
existed. What I thought you were getting at was the condition to decide if we
should use the in-memory checksum or not (which is what you describe).
3. If we don't put the sync set/get method in ReplicaInPipelineInterface, we
will have to use an if/else construct on instanceof in BlockReceiver and call
one or the other. I can see the argument for keeping the method out of the
interface since it is RBW-specific, but on the other hand, it's effectively a
no-op for other implementers of the interface and leads to cleaner code (better
natural polymorphism then if-else constructs to force it).
either way, just wanted to throw that out there as a question of style
> 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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