Head-of-Line Blocking (队头堵塞)

Abstract

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• When one object blocks other or following object from progressing

HTTP Head-of-Line Blocking

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• Happens when there is only one single TCP Connection like HTTP 1.0
• Below shows when we aren’t able to receive the CSS file. We aren’t able to request for the JS file. Thus, the CSS file is blocking other files in the queue from be requested & received

Software Solution

1. Having different domains serving different object, the browser will have a different TCP Connection with each domain. Thus, if one HTTP Request failed, it doesn’t block browser from retrieving object from other domains
2. Technologies like Webpackto consolidate many Object into a few Object

Networking Solution

• HTTP Multiplexing (多路复用)

TCP Head-of-Line Blocking

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• When one of the many TCP Segment is lost, we need to wait for it to be resent & receive, in order to proceed with the receiving of the rest of the TCP Segment
• All the HTTP Response in that TCP Connection is blocked!

Solved by HTTP 1.3 QUIC