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Comment by lxe | Hacker News Reader

> So, if we’ve already got ~40 milliseconds of round-trip network latency in the first place, will our users be able to perceive the difference in a web application which renders a response in 1 millisecond or 100 milliseconds? That is, one application will take 41 milliseconds in total and the other 141.

Yes. Definitely. Absolutely. The users will perceive the difference. This is a slowdown of over 3X. If you're loading resources (in a variety of synchronous batches of asynchronous requests) for your web application, these slowdowns compound significantly.

Of course, the design of the web application plays a huge role, but assuming the worst (every user action triggers a request), a 3X slowdown is perceived by a variety of users.

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If you're talking about humans, absolute time is much more important than "3X". Everybody would notice the difference between 1 second and 3 seconds. Nobody would notice the difference between 1 ms and 3 ms. 100ms is perceivable, but not a problem in most situations involving a web request.

I think your making a strong point here, that might not get the attention it deserves.

> asynchronous requests

Because we don't live in a world where one user loads one page and then loads the next one (and if they do we should be talking about how your not using cached static content).

If I can do the work in 20ms, and it takes 100ms with framework overhead what happens when these start stacking up?

Not only do those things impact the user they impact your server... every ms that it has to maintain that connection, do work is one more ms that it isn't doing work for someone else.

I cited decades of human-computer interaction research that disagrees with you.

EDIT: also, that paragraph is purely discussing the response times for producing the HTML document of a web application, not, say if you added 100ms lag to every JS response (which would compound, like you say).

I think one of the main datapoints is the classic quote from Amazon that 100ms of added latency reduces sales by 1%. There are similar comments floating around from other big players (Google etc) too.

edit: this is the best link I could find for now: http://highscalability.com/latency-everywhere-and-it-costs-y...

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