Binglin Chang created HADOOP-8990:
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             Summary: Some minor issus in protobuf based ipc
                 Key: HADOOP-8990
                 URL: https://issues.apache.org/jira/browse/HADOOP-8990
             Project: Hadoop Common
          Issue Type: Improvement
            Reporter: Binglin Chang
            Priority: Minor


1. proto file naming
RpcPayloadHeader.proto include not only RpcPayLoadHeader, but also 
RpcResponseHeaderProto, which is irrelevant to the file name.
hadoop_rpc.proto only include HadoopRpcRequestProto, and the filename 
"hadoop_rpc" is strange comparing to other .proto file names.
How about merge those two file into HadoopRpc.proto?

2. proto class naming
In rpc request RpcPayloadHeader includes callId, but in rpc response callId is 
included in RpcResponseHeader, and there is also HadoopRpcRequestHeader, this 
is just too confusing.

3. The rpc system is not fully protobuf based, there are still some Writables:
RpcRequestWritable and RpcResponseWritable.
rpc response exception name and stack trace string.
And RpcRequestWritable uses protobuf style varint32 prefix, but 
RpcResponseWritable uses int32 prefix, why this inconsistency?

Currently rpc request is splitted into length, PayLoadHeader and PayLoad, and 
response into RpcResponseHeader, response and error message. 
I think wrap request and response into single RequstProto and ResponseProto is 
better, cause this gives a formal complete wire format definition, 
or developer need to look into the source code and hard coding the 
communication format.

These issues above make it very confusing and hard for developers to use these 
rpc interfaces.

Some of these issues can be solved without breaking compatibility, but some can 
not, but at least we need to know what will be changed and what will stay 
stable?



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