Schedulers.io() provides us with I/O bound threads. To be more accurate, Schedulers.io() provides you with ThreadPool, which can create an unbounded number of worker threads that are meant to be performing I/O bounded tasks.

Now, what exactly does the I/O bounded thread mean? And why are we calling it I/O bounded? Let's inspect.

All the threads in this pool are blocking and are meant to perform more I/O operations than computationally intense tasks, giving less load to CPUs, but may take longer due to waiting for I/O. By I/O operations, we mean interactions with file systems, databases, services, or I/O devices.

We should be cautious about using this scheduler as it can create an infinite number of threads (until the memory lasts) and can cause OutOfMemory errors.