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https://issues.apache.org/jira/browse/HDFS-1123?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Jay Booth updated HDFS-1123:
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Attachment: datanode-reads.txt
Here's a first pass at the protocol for reading from a DataNode. Tried to be
pretty thorough, but it could probably use clarification in a few places and
might have an error. Could definitely use checking for style. Should we put
this on a wiki somewhere?
The NameNode part of the process is entirely ipc.Server derived with Writables,
I believe, so for that item API and conceptual documentation is probably more
useful than an itemized description of each writable type.
> Need HDFS Protocol Specification
> --------------------------------
>
> Key: HDFS-1123
> URL: https://issues.apache.org/jira/browse/HDFS-1123
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: documentation
> Reporter: bc Wong
> Attachments: datanode-reads.txt
>
>
> It'd be great to document (in a spec, not in the code) the HDFS wire protocol:
> * The layout of the different request and reply messages.
> * The semantics of the various calls.
> * The semantics of the various fields.
> For example, I stumbled upon the goldmine of comments around
> DataNode.java:1150. It looks correct, but the version number of 9 doesn't
> inspire confidence that it's up-to-date. (It's also a random place to put
> such an important comment.)
> Having a formal spec is a big step forward for compatibility. It also
> highlights design decisions and helps with protocol evolution.
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