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I have multiple AJAX requests going out of my browser. My UI is comprised of multiple views and the AJAX requests are trying to populate those views simultaneously. In some cases I require more than 10 simultaneous requests to be sent from client and processed concurrently at the server.

But due to browser limitations on max concurrent requests to a single domain and because of HTTP's "A server MUST send its responses to requests in the same order that the requests were received" constraint, I am not deriving as much concurrency in request processing as I would want.

From my application's standpoint, I dont need responses to come in the order in which I sent the request. I am ok if view8 gets populated before view1, for example.

Async processing using Servlet 3.0 constructs seems to address only one-side of the problem (the Server-side) and hence cannot be fully exploited for maximizing application concurrency.

My question is: Am I missing out on some proper constructs ? ('proper' in contrast to workarounds like "host your images from a different sub domain") that can yield me more concurrency ?

This seems like something many web UIs would need ! If not, then I am designing my UI the wrong way. In either case, I would appreciate your inputs.

Edit1: To my advantage, I dont have to support a huge number of concurrent clients. The maximum number of concurrent clients accessing the app would be < 100. Given that fact, basically am trying to enhance the experience of these clients when I have the processing power available aplenty on my server-side.

Edit2: Our application/API is not for 'public' consumption. For ex: It is like my company's webmail app. It is hosted on the internet but it is not meant for everyone's consumption. Only meant for consumption by the relevant few. The reason why am giving that info, is to differentiate my app from SO/Twitter, which seem to differentiate their (REST) API users from their normal website users. In our case, we think we should not differentiate that way and want to provide single-set of REST endpoints for both.

The reason behind the limitation in the spec (RFC2616) seems to be : "These guidelines are intended to improve HTTP response and avoid congestion.". However, intranet web apps have more luxuries and should not have to be so constrained !?

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2020
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  • 10 concurrent AJAX requests sound a bit too much. Any reason why you can't collate them together given they need to be sent out *simultaneously*? Or is it that you are using some sort of JEE framework and the requests are not in your control? – Sanjay T. Sharma Apr 04 '13 at 18:05
  • The server is exposing REST API and hence the UI makes specific GETs for various resource catogories (ex: blogs, videos, news, articles). Since each resource catogory has its exclusive view it all fits in nicely. It feels wrong to collate requests to get blogs and videos together in one request. Isnt it ? – 2020 Apr 04 '13 at 18:10
  • Well, IMHO being pragmatic is more important. Sure, it makes sense for a service to expose RESTful API but it's not always necessary to expose the entire API to the browser. Your API can be separate from your server side web app. You can always make those multiple API requests on the server side, collate the results and send them back to the client. For e.g. look at the SO home page. The StackOverflow API *does* expose a RESTful API but when loading the home page the browser doesn't send across multiple requests just to populate the tags, thread listing etc. – Sanjay T. Sharma Apr 04 '13 at 18:56
  • Thanks Sanjay for the suggestion. But we wanted to have a single-API for both REST clients and Browser clients. Interestingly, the root URI "stackoverflow.com" is not mentioned in SO's REST API, but the browser client uses it. I suppose if they had exposed the root URI, their response would be difficult to process (as it would be a mixture of data). Their REST API is granular (as is in my application), but their javascript code uses some other doors(APIs) to decrease no. of round-trips to the server! Somehow that doesnt feel right (Am a novice in this field though). Feel free to correct me. – 2020 Apr 04 '13 at 21:40
  • SO doesn't use any "other doors". It's just that they simply don't send across 10 concurrent requests for populating something on the page. They make XHR request when you vote, mark thread as favorite, comment etc. For loading the page itself, there are no multiple requests. If you want to directly hit your RESTful API from the browser, you'll have to honor the limitations. Either that or go the desktop way which allows you virtually unlimited connections to your server but I guess you don't want to go that route... – Sanjay T. Sharma Apr 05 '13 at 06:03
  • Hello Sanjay, your comments have been very insightful. I think it is only fair that you post an answer so that it gets the due credit ! Thanks ! – 2020 Apr 05 '13 at 17:25
  • I have moved our discussion to an answer for better visibility to others. Good luck! – Sanjay T. Sharma Apr 05 '13 at 17:39

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The server is exposing REST API and hence the UI makes specific GETs for various resource catogories (ex: blogs, videos, news, articles). Since each resource catogory has its exclusive view it all fits in nicely. It feels wrong to collate requests to get blogs and videos together in one request. Isnt it ?

Well, IMHO being pragmatic is more important. Sure, it makes sense for a service to expose RESTful API but it's not always necessary to expose the entire API to the browser. Your API can be separate from your server side web app. You can always make those multiple API requests on the server side, collate the results and send them back to the client. For e.g. look at the SO home page. The StackOverflow API does expose a RESTful API but when loading the home page the browser doesn't send across multiple requests just to populate the tags, thread listing etc.

Thanks Sanjay for the suggestion. But we wanted to have a single-API for both REST clients and Browser clients. Interestingly, the root URI "stackoverflow.com" is not mentioned in SO's REST API, but the browser client uses it. I suppose if they had exposed the root URI, their response would be difficult to process (as it would be a mixture of data). Their REST API is granular (as is in my application), but their javascript code uses some other doors(APIs) to decrease no. of round-trips to the server! Somehow that doesnt feel right (Am a novice in this field though). Feel free to correct me

SO doesn't use any "other doors". It's just that they simply don't send across 10 concurrent requests for populating something on the page. They make XHR request when you vote, mark thread as favorite, comment etc. For loading the page itself, there are no multiple requests. If you want to directly hit your RESTful API from the browser, you'll have to honor the limitations. Either that or go the desktop way which allows you virtually unlimited connections to your server but I guess you don't want to go that route...

Sanjay T. Sharma
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  • While you gave insight on the need to avoid so many concurrent AJAX requests, the other part of my question regarding out-of-order responses is still unresolved. I have created [a different question](http://stackoverflow.com/questions/16288102/is-it-possible-to-receive-out-of-order-responses-with-http) for it. Request your comments on it. – 2020 Apr 29 '13 at 22:44