通过 HTTP2 批处理请求

Question

Is it possible to get a better throughput from our servers, if we make one large HTTP request, as opposed to multiple smaller HTTP requests over HTTP2.

As per my understanding it should not produce any significant difference in performance since with HTTP2 we can have multiple requests multiplexed over one TCP connection.

Answer 1

Yes at a network level one large request will be more efficient than multiple small requests. This is due to the overhead of making a network request.

This is also why concatenating CSS and JavaScript and spriting for images were recommended under HTTP/1.1 so the amount of data sent was the same, but the amount of requests was considerably lower. In fact due to the way compression like gzip works the amount of data was often smaller when sending large requests.

HTTP/2 was designed to make the costs of HTTP requests a lot smaller though the reuse of a single TCP connection using multiplexing . In theory this would allow us to give up concatenation and spriting. The reality has been a little less than perfect though - usually due to browser inefficiencies rather than HTTP/2's fault. The bottleneck has just moved and we need to optimise browsers for the new world. So, for now, some level of concenation and spriting is still recommended.

Getting back to your question, then yes it should have single effects at that network level and in fact HTTP/1.1 and HTTP/2 may even be similar in performance if you do this.

However beyond the network level you may discover other reasons not to bundle into fewer files. If you have one large JavaScript file for example then the browser must wait for it all to be downloaded before it can be parsed, compiled and run. You may be better getting smaller, more important JavaScript downloaded first. Similarly with image spriting you may be waiting for the entire sprite file to download before a single image is display.

Then there are the caching implications. Changing a single line of JS or adding a single image to the image Sprite requires creating a whole new large file, meaning the older one cannot be used and the whole thing needs to be downloaded again in its entirety.

Plus having large files can be more complicated to implemented and managed. They require a build step (maybe not a big deal as many sites do) and creating and managing image sprites through CSS is often more difficult.

Also if using this to stick with HTTP/1.1, then you may be missing out on are the other benefits of HTTP/2 including HPACK header compression and HTTP/2 push (though this is also more tricky to get right than initially thought/hoped!).

It's a fascinating topic that I've spent a lot of time on , and best advice (as always!) is to understand the technology and test, test, test!