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https://issues.apache.org/jira/browse/HDFS-2288?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13236220#comment-13236220
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Eli Collins commented on HDFS-2288:
-----------------------------------
There's two definition of visible length, or rather we're using the same name
for two things:
1. The above definition by Konst and the design doc which defines it as
property of the replica:
{quote}
visible length is the "number of bytes that have been acknowledged by the
downstream DataNodes". It is replica (not block) specific, meaning it can be
different for different replicas at a given time. In the document it is called
BA (bytes acknowledged), compared to BR (bytes received).
{quote}
2. Nicholas' definition in HDFS-814 and DFSClient#getVisibleLength which
defines it as a property of a file:
{quote}
The visible length is the length that *all* datanodes in the pipeline contain
at least such amount of data. Therefore, these data are visible to the readers.
{quote}
According to this definition the visible length of a file is the floor of all
visible lengths of all the replicas of the last block. It's a static property
set on open, eg is not updated when a writer calls hflush. Also
DFSInputStream#readBlockLength returns the 1st visible length of a replica it
finds, so it seems possible (though unlikely) in a failure scenario it could
return a length that was longer than what all replicas had.
Perhaps we should rename DFSClient#getVisibleLength?
> 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
> 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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