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https://issues.apache.org/jira/browse/HADOOP-18536?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17637036#comment-17637036
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xinqiu.hu commented on HADOOP-18536:
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Thank you very much for reviewing the code, I agree with the risk you said.
But RPC Client is not only used in hdfs client, it is used in almost every
component of hadoop, such as Application Master, DataNode, Yarn Node Manager,
Container. If each request can reduce the allocation of 1024 bytes, I think
there is a certain gain.
And this idea didn't come out of thin air, it came from
ipc.Server#setupResponseForProtobuf and ipc.Server#setupResponseForWritable.
> RPC Client Improvement
> ----------------------
>
> Key: HADOOP-18536
> URL: https://issues.apache.org/jira/browse/HADOOP-18536
> Project: Hadoop Common
> Issue Type: Improvement
> Components: rpc-server
> Reporter: xinqiu.hu
> Priority: Minor
>
> In the RPC Client, before a request (including RpcRequestHeaderProto,
> RequestHeaderProto, Message Payload) is sent, they will be copied to the three
> CodedOutputStream internal byte arrays, and then aggregated to the
> ResponseBuffer
> internal byte array. Then the ResponseBuffer byte array is written to a
> BufferedOutputStream and finally to a SocketOutputStream.
> To simplify the writing process, Maybe we can copy them directly to a big
> CodedOutputStream and send them directly to the IpcStreams#out. To achieve
> this, I
> propose HADOOP-18533. But it brings the following two side effects.
> # The generic declaration of rpcRequestQueue inside Client has been changed
> to Object
> # The serialization of protobuf has been moved to rpcRequestThread, because
> rpcRequestThread is a single thread for each connection, which may have a
> performance impact.
> For the above reasons, I propose this. This pr brings the following benefits
> # For each rpc request, avoid creating a ResponseBuffer of 1024 bytes
> # For each rpc request, reduce one copy
> # For each rpc request, combine the three fragmented CodedOutputStreams into
> one
> # No side effects like HADOOP-18533
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