Yes. By default 4 is threadpool size however it can be increased.
In order to change the threadpool size , modify your program
process.env.UV_THREADPOOL_SIZE=64
//then execute some function that requires threadpool
require('fs').readFile('loadtest',function(){});
Today’s operating systems already provide asynchronous interfaces
for many I/O tasks. (Example: AIO on linux)
Whenever possible, libuv will use those async interfaces avoiding usage of
threadpool.Only if there is no other way, the thread pool will be used
for async I/O