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https://issues.apache.org/jira/browse/HDFS-2288?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13095668#comment-13095668
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Tsz Wo (Nicholas), SZE commented on HDFS-2288:
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{quote}
If all of the DNs crashed at the same time, and the client didn't update
the generation stamp, then the replicas may have different lengths. But, all of
the replicas are at least as long as the last successful fsync, which is the
only guarantee we have to provide.
{quote}
We also provide read consistency, i.e. if N bytes are successful read from one
datanode, then the same N bytes are available from all datanodes in the
pipeline so that the client can switch to other datanodes and continue reading.
If the replicas have different lengths and client is reading from the datanode
with longest length, then it continue reading from the other datanodes.
> Replicas awaiting recovery should return a full visible length
> --------------------------------------------------------------
>
> Key: HDFS-2288
> URL: https://issues.apache.org/jira/browse/HDFS-2288
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: data-node
> Affects Versions: 0.23.0
> Reporter: Todd Lipcon
> Assignee: Todd Lipcon
> Priority: Critical
> Fix For: 0.23.0
>
> Attachments: hdfs-2288.txt
>
>
> Currently, if the client calls getReplicaVisibleLength for a RWR, it returns
> a visible length of 0. This causes one of HBase's tests to fail, and I
> believe it's incorrect behavior.
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