A reasonable number of simultaneous, asynchronous ajax requests

Question

I'm wondering what the consensus is on how many simultaneous asynchronous ajax requests is generally allowable.

The reason I ask, is I'm working on a personal web app. For the most part I keep my requests down to one. However there are a few situations where I send up to 4 requests simultaneously. This causes a bit of delay, as the browser will only handle 2 at a time.

The delay is not a problem in terms of usability, for now. And it'll be awhile before I have to worry about scalability, if ever. But I am trying to adhere to best practices, as much as is reasonable. What are your thoughts? Is 4 requests a reasonable number?

Answer 1

I'm pretty sure the browser limits the number of connections you can have anyway.

If you have Firefox, type in about:config and look for network.http.max-connections-per-server and that will tell you your maximum. I'm almost positive that this will be the limit for AJAX connections as well. I think IE is limited to 2. I'm not sure about Chrome or Opera.

Edit:

In Firefox 23 the preference with name network.http.max-connections-per-server doesn't exist, but there is a network.http.max-persistent-connections-per-server and the default value is 6.

Answer 2

That really depends on if it works like that properly. If the logic of the application is built that 4 simultaneos requests make sense, do it like this. If the logic isn't disturbed by packing multiple requests into one request you can do that, but only if it won't make the code more complicated. Keep it as simple and straight forward until you have problems, then you can start to optimize.

But you can ask yourself if the design of the app can be improved that there is no need for multiple requests.

Also check it on a really slow connection. Simultaneous http requests are not necessarily executed on the server in the proper order and they might also return in a different order. That might give problems you'll experience only on slower lines.