Support for options within the inter-datanode protocol
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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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