Can an isolate handle multiple requests at once? (For example, suppose there are lots of cheap requests, so it's I/O bound, not CPU bound.)
How much extra memory usage is there per isolate?
How much extra memory usage is there per isolate?
The main isolate creates an Application instance that has N number of supervisors, one for each isolate. The isolates are launched and go thru their initialization steps, reporting back to their supervisor. The application completes its launch once all supervisors have reported back. It fails its launch if an isolate throws an error during initialization or does not hear back in a configurable timeout. Any inter-isolate messages sent during startup are queued until all isolates have completed startup.
Once the isolates are up and running, the main isolate doesn't do anything other than facilitate the inter-isolate message hub. Requests are delivered directly to the isolates running the web server.
When running automated tests, the default behavior is to run everything on the main isolate, since tests are run against a temporary database schema that only exists for the lifetime of the connection.
The memory consumption of an isolate depends on the size of the application code. Each isolate actually has its own copy of the application code that gets tuned by the VM over time. Even stuff like static variables are per-isolate. I just pulled up an OK sized Aqueduct project, and it looks like about 30-40MB per isolate. Most of that is probably Aqueduct itself. A worker isolate is likely an order of magnitude smaller.
1: https://webdev.dartlang.org/articles/performance/event-loop