[GitHub] [rocketmq] MountainOne commented on issue #1510: Some question about "vip channel"?

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MountainOne commented on issue #1510: Some question about "vip channel"?
URL: https://github.com/apache/rocketmq/issues/1510#issuecomment-543606739
 
 
   `brokerVIPChannel` will return 2 possible broker's addresses. One is the origin address which has been passed in, another is an address with a different port. For example:
   `brokerVIPChannel(true, "127.0.0.1:9876") -> "127.0.0.1:9874"
    brokerVIPChannel(false, "127.0.0.1:9876") -> "127.0.0.1:9876"
   `
   The origin one is the normal channel and the different one is the VIP channel.
   BrokerController will initialize 2 NettyRemotingServer instance when a broker starts with the same configuration, whick means these 2 server instances listening 2 different port has the same function. In other words, the VIP channel has the same function with the normal channel.
   So why broker needs 2 server instance?
   The answer is to isolate the read and write operation. Among the API of the message , the most important one is sending message which requires high RTT . It will block netty's IO thread when it occurs message accumulation and impact to write link . The request for consuming message will full of the IO thread pool which will result in the write operation are blocked . In this case , we could send message to VIP channel to guarantee the RTT of sending messages .

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