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https://issues.apache.org/jira/browse/HADOOP-4096?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12628803#action_12628803
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Tsz Wo (Nicholas), SZE commented on HADOOP-4096:
------------------------------------------------
Do you mean "Datanode transfer protocol", i.e. the protocol described in
DataNode.java line 916 - 995? Inter-datanode protocol is another protocol
defined in org.apache.hadoop.hdfs.server.protocol.InterDatanodeProtocol.
> Support for options within the inter-datanode protocol
> ------------------------------------------------------
>
> Key: HADOOP-4096
> URL: https://issues.apache.org/jira/browse/HADOOP-4096
> Project: Hadoop Core
> Issue Type: New Feature
> Components: dfs
> Reporter: George Porter
>
> This proposal is to extend the streaming inter-datanode protocol to support
> "options", in the spirit of IP or TCP options. This should make this
> protocol more extensible, allowing the client to include metadata along with
> commands. This would support efforts to include end-to-end and causal
> tracing into Hadoop, and hopefully other efforts as well.
> Options should have a type, and be of variable length. It should be possible
> to include multiple options along with each datanode command. The option
> should apply to both the command and any data that is part of the command.
> If the datanode does not understand a given option, it should ignore it.
> Options should be sent end-to-end through intermediate datanodes, if
> necessary. For example, if an OP_WRITE_BLOCK command is pipelined through
> several machines, the options should be sent along the pipeline. Nodes along
> the pipeline may modify the options.
> BTW, If HADOOP-4005 (concrete datanode protocol) is implemented, then it
> should solve this problem by simply letting the user add state to the
> concrete protocol class.
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