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For what it's worth, Google App Engine uses a so-called "intelligent" global request queue/scheduler. In most circumstances it's quite effective.

It is effective, but not without problems.

Needless to say, it is VASTLY better than Heroku's router. You'll never see an H12 error with GAE.

Indeed, while having a global request queue is good, the scheduler's one-size-fits-all behavior can sometimes be suboptimal. Thankfully there are several ways in which it can be tuned: https://developers.google.com/appengine/docs/adminconsole/pe...

Source please?

"Pending request latency arises when all of your application's available instances are too busy to serve new requests. When this happens, incoming requests go to a pending request queue." https://developers.google.com/appengine/docs/adminconsole/pe...

Pending latency is exposed as a metric on the App Engine Dashboard.