[jira] Commented: (HDFS-1058) reading from file under construction fails if it reader beats writer to DN for new block

["Thanh Do (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HDFS-1058?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12965545#action_12965545 ] 

Thanh Do commented on HDFS-1058:
--------------------------------

I think this is a design decision (stated in append design document at HDFS-265)
Here we trade performance for consistency,


> reading from file under construction fails if it reader beats writer to DN for new block
> ----------------------------------------------------------------------------------------
>
>                 Key: HDFS-1058
>                 URL: https://issues.apache.org/jira/browse/HDFS-1058
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>          Components: data-node, hdfs client
>    Affects Versions: 0.21.0, 0.22.0
>            Reporter: Todd Lipcon
>
> If there is a writer and concurrent reader, the following can occur:
> - The writer allocates a new block from the NN
> - The reader calls getBlockLocations
> - Reader connects to the DN and calls getReplicaVisibleLength
> - writer still has not talked to the DN, so DN doesn't know about the block and throws an error

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