You're right, in principle. However, rewriting it in C++ instead of Java would maybe get you a factor of 2 performance improvement, and that's if it was completely CPU-bound, which isn't a reasonable assumption for a tool designed to manage large disk-resident datasets.

By "hard real-time" I was referring to latency, rather than throughput. Achieving very low latencies is difficult in Java because you don't know exactly when the GC will kick in, but nevertheless it's possible to get very high throughput.