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https://issues.apache.org/jira/browse/HDFS-4452?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13565891#comment-13565891
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Konstantin Shvachko commented on HDFS-4452:
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Marked it critical. Saw it happening on a large cluster under load.
Up to RM to make it a blocker at this point. Lohit you can always lobby for it.
Brandon, adding the offset parameter to addBlock() is the right direction. I
was also thinking making the first synchronized section as a read-only and use
writeLock only when actually adding the block. Under this approach it may be
acceptable to move chooseTarget under the readLock of the first section.
> getAdditionalBlock() can create multiple blocks if the client times out and
> retries.
> ------------------------------------------------------------------------------------
>
> Key: HDFS-4452
> URL: https://issues.apache.org/jira/browse/HDFS-4452
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: namenode
> Affects Versions: 2.0.2-alpha
> Reporter: Konstantin Shvachko
> Assignee: Konstantin Shvachko
> Priority: Critical
> Attachments: TestAddBlockRetry.java
>
>
> HDFS client tries to addBlock() to a file. If NameNode is busy the client can
> timeout and will reissue the same request again. The two requests will race
> with each other in {{FSNamesystem.getAdditionalBlock()}}, which can result in
> creating two new blocks on the NameNode while the client will know of only
> one of them. This eventually results in {{NotReplicatedYetException}} because
> the extra block is never reported by any DataNode, which stalls file creation
> and puts it in invalid state with an empty block in the middle.
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