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https://issues.apache.org/jira/browse/SPARK-21703?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16123071#comment-16123071
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neoremind commented on SPARK-21703:
-----------------------------------
Thanks Sean to guide me to the right place. Here's the
[link](http://apache-spark-user-list.1001560.n3.nabble.com/SPARK-CORE-Why-RPC-message-are-transferred-with-header-and-body-separately-in-TCP-frame-td29054.html).
> 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 why to implement in
> such way? Thanks!
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