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https://issues.apache.org/jira/browse/HDFS-3219?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13248649#comment-13248649
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Tsz Wo (Nicholas), SZE commented on HDFS-3219:
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Consider the permission of file. User can change it any time. When the
getFileStatus is called, the value of permission at that time is returned. If
the user further changes the permission, the value returned won't be updated.
The so-called static/dynamic property of visible length should be understood
like this.
> Disambiguate "visible length" in the code and docs
> --------------------------------------------------
>
> Key: HDFS-3219
> URL: https://issues.apache.org/jira/browse/HDFS-3219
> Project: Hadoop HDFS
> Issue Type: Improvement
> Reporter: Eli Collins
> Priority: Minor
>
> HDFS-2288 there are two definition of visible length, or rather we're using
> the same name for two things:
> 1. The HDFS-265 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. The 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.
> This has caused confusion in a number of other jiras. We should update the
> design doc, java doc, perhaps rename DFSClient#getVisibleLength etc to
> disambiguate this.
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