For the millionth time: It is not accurate to refer to it as single threaded.

The language is non-blocking, so any asynchronous tasks (DB read/writes, disc I/O, cache, http, etc) will immediately jump to processing the next request the moment it is not doing blocking computation.

Non-blocking:

    [aa][bb][cc][/aa][/cc][/bb][dd][ee][ff][gg][/dd][/ff][/gg][/ee]

Blocking-threaded:

    [aa]------------------------[/aa][ff]----------------------[/ff]

    [bb]------------------------[/bb][gg]----------------------[/gg]
    
    [cc]------------------------[/cc][ee]----------------------[/ee]
    
    [dd]------------------------[/dd]

Depending on how many threads you can get going at once, you may be able to achieve comparable performance doing threading, but nonblocking is basically leaving 0 time on the core wasted and limited to the speed of the event loop.

And then on top of that, clustering module is used to do the same thing on every core.