I had to spend some time dealing with the performance of a long-running simulation. The biggest issue was that long-term mining in the system created very complex asteroids that were heavy to simulate. Therefore, I introduced a simplified form of debris. When nothing is too close, I switch to this simplified form. This really lightens the load on the physics engine. Now I can have a solar system with thousands of asteroids without any problems.

Another problem was a bug in Sticker behavior. These little creatures did not avoid the Sun, so they eventually ended up inside it. That caused a massive spike in collisions and really choked the physics engine. The fix was quite simple: improve their avoidance and also let them burn like everything else.