That's the big question I have too. I think typically it's I/O in one form or another. With GPUs sending data to the GPU seems to be another cost in the path.

That's the big question I have too. I think typically it's I/O in one form or another. With GPUs sending data to the GPU seems to be another cost in the path. However if you consider the GPU part as a way to push down processing power close to data, then you can probably solve more complex problems like graph processing efficiently within the DB..