What happens if an application calls more than 10 asynchronous URL Fetch on Google App Engine?

Question

Reading the Google App Engine documentation on asynchronous URL Fetch:

The app can have up to 10 simultaneous asynchronous URL Fetch calls

Answer 1

500 errors start happening. Silently.

You only find out about these when you look at your log under all requests (don't get listed as errors). It simply says "The request was aborted because you reached your simultaneous requests limit".

So when you're making lots of asynchronous calls, make sure you can handle some of them spazzing out.