WebAPI Lifecycle/Request Queue

Question

I have an AngularJS app that calls WebAPI. If I log the time I initiatiate a request (in my angluar controller) and log the time OnActionExecuting runs (in an action filter in my WebAPI controller), I notice at times a ~2 second gap. I'm assuming nothing else is running before this filter and this is due to requests being blocked/queued. The reason I assume this is because if I remove all my other data calls, I do not see this gap.

What is the number of parallel requests that WebAPI can handle at once? I tried looking at the ASP.NET performance monitors but couldn't find where I could see this data. Can someone shed some insight into this?

Answer 1

There's no straight answer for this but the shortest one is ...

There is no limit to this for WebApi the limits come from what your server can handle and how efficient the code you have it run is.

... But since you asked, lets consider some basic things that we can assume about our server and our application ...

1. concurrent connections

A typical server is known for issues like "c10k" ... https://en.wikipedia.org/wiki/C10k_problem ...so that puts a hard limit on the number of concurrent connections.

Assuming each WebApi call is made from say, some AJAX call on a web page, that gives us a limit of around 10k connections before things get evil.

2.Dependency related overheads

If we then consider the complexity of the code in question you may then have a bottleneck in doing things like SQL queries, I have often written WebApi controllers that have business logic that runs 10+ db queries, the overhead here may be your problem?

3. Feed in Overhead

What about network bandwidth to the server? Lets assume we are streaming 1MB of data for each call, it wont take long to choke a 1Gb/s ethernet line with messages that size.

4. Processing Overhead

Assuming you wrote an Api that does complex calculations (e.g mesh generation for complex 3D data) you could easily choke your CPU for some time on each request.

5. Timeouts

Assuming the server could accept your request and the request was made asynchronously the biggest issue then is, how long are you prepared to wait for your response? Assuming this is quite short you would reduce the number of problems you have time to solve before each request then needed a response.

...

So as you can see, this is by no means an exhaustive list but it outlines the complexity of the question you asked. That said, I would argue that WebApi (the framework) has no limits, it's really down to the infrastructure around it that has limitations in order to determine what can be possible.