In theory, yes. Rays get bounced around from a light source until they hit a camera (or decay below a threshold). The net intensity is recorded for all the rays

In theory, yes. Rays get bounced around from a light source until they hit a camera (or decay below a threshold). The net intensity is recorded for all the rays in the camera plane. Computing the net intensity is a reduction over all the rays hitting that pixel in the camera plane. Then you have NUM_BOUNCES many map steps to compute the position and intensity of the ray after each bounce. So in theory these map and reduce operations could be expressed in a database context. In practice, does it make sense? Not really since each ray is not the same amount of work. One ray can go straight to the camera. Another could bounce many, many times going through many objects before hitting the camera or dying out altogether. GPUs are terrible at handling workloads with high thread divergence (some threads run much slower than others).