Head-of-Line Blocking (队头堵塞)

Abstract

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• When one object blocks other object 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
• Above 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

Solution

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 Webpack consolidate many Object into a few object to minimise the chance of blocking

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!

Solution

Solved by HTTP 1.3.