ReferenceGlossary
Async I/O
A way to start a network or disk operation and do other work until it completes, instead of blocking a thread while it waits. One thread can then keep many requests in flight. Node.js, .NET async, and Rust's Tokio are built on it.
Runtimes
In Quorum#
Node.js, Kestrel (C#), and Tokio (Rust) hold no worker slot while a request waits for the Database, so a slow query does not use up their capacity. A PHP-FPM or Gunicorn worker is held for the whole wait. Async runtimes also keep Realtime connections open for a few KB each (Tokio 5 KB, Node.js 20 KB), while PHP and Gunicorn refuse them.
Read next#
Event loop, Green threads, Process per request, Little's law