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https://issues.apache.org/jira/browse/HDFS-9607?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15120280#comment-15120280
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Konstantin Shvachko commented on HDFS-9607:
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> Even though HDFS files stores bytes, from a users perspective, these bytes
> could be finance data or personal contact
Dinesh, this is an application-level logic. HDFS has no knowledge of the
semantics of the bytes it stores. It does not know how the data is structured,
what are the delimiters, if data is compressed, encrypted, serialized, etc.
Just ask yourself how you would implement your own {{canWrite()}} method on the
HDFS level.
User can do everything you are talking about by reading, and comparing stored
data with new values. The only think missing is the ability to update bytes in
an HDFS file. The positional write method I suggested
[earlier|https://issues.apache.org/jira/browse/HDFS-9607?focusedCommentId=15088000&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-15088000]
> Advance Hadoop Architecture (AHA) - HDFS Update (write-in-place)
> ----------------------------------------------------------------
>
> Key: HDFS-9607
> URL: https://issues.apache.org/jira/browse/HDFS-9607
> Project: Hadoop HDFS
> Issue Type: New Feature
> Reporter: Dinesh S. Atreya
>
> Link to Umbrella JIRA
> https://issues.apache.org/jira/browse/HADOOP-12620
> Provide capability to carry out in-place writes/updates. Only writes in-place
> are supported where the existing length does not change.
> For example, "Hello World" can be replaced by "Hello HDFS!"
> See
> https://issues.apache.org/jira/browse/HADOOP-12620?focusedCommentId=15046300&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-15046300
> for more details.
> Currently following are supported.
> # Sequential writes
> # Append (HADOOP-1700, HDFS-265)
> # Snapshots (HDFS-2802)
> # Truncate (HDFS-3107)
> This JIRA is for random updates (write-in-place).
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