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https://issues.apache.org/jira/browse/SPARK-21703?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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neoremind updated SPARK-21703:
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    Description: 
After seeing the details of how spark leverage netty, I found one question, 
typically RPC message wire format would have a header+payload structure, and 
netty uses a TransportFrameDecoder to deal with how to determine a complete 
message from remote peer. But after using Wireshark sniffing tool, I found that 
the message are sent separately with header and then followed by body, although 
this works fine, but for underlying TCP there would be ACK segments sent back 
to acknowledge, there might be a little bit redundancy since we can sent them 
together and the header are usually very small. 

The main reason can be found in MessageWithHeader class, since transferTo 
method write tow times for header and body.

Could someone help me understand the background story on how to implement in 
such way?  Thanks!

  was:
After seeing the details of how spark leverage netty, I found one question, 
typically RPC message wire format would have a header+payload structure, and 
netty uses a TransportFrameDecoder to deal with how to determine a complete 
message from remote peer. But after using Wireshark sniffing tool, I found that 
the message are sent separately with header and then followed by body, although 
this works fine, but for underlying TCP there would be ACK segments sent back 
to acknowledge, there might be a little bit redundancy since we can sent them 
together and the header are usually very small. 

The main reason can be found in MessageWithHeader class, since transferTo 
method write tow times for header and body.

Could some one help me understand the background story on how to implement in 
such way?  Thanks!


> Why RPC message are transferred with header and body separately in TCP frame
> ----------------------------------------------------------------------------
>
>                 Key: SPARK-21703
>                 URL: https://issues.apache.org/jira/browse/SPARK-21703
>             Project: Spark
>          Issue Type: Question
>          Components: Spark Core
>    Affects Versions: 1.6.0
>            Reporter: neoremind
>            Priority: Trivial
>              Labels: RPC
>
> After seeing the details of how spark leverage netty, I found one question, 
> typically RPC message wire format would have a header+payload structure, and 
> netty uses a TransportFrameDecoder to deal with how to determine a complete 
> message from remote peer. But after using Wireshark sniffing tool, I found 
> that the message are sent separately with header and then followed by body, 
> although this works fine, but for underlying TCP there would be ACK segments 
> sent back to acknowledge, there might be a little bit redundancy since we can 
> sent them together and the header are usually very small. 
> The main reason can be found in MessageWithHeader class, since transferTo 
> method write tow times for header and body.
> Could someone help me understand the background story on how to implement in 
> such way?  Thanks!



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