Yes it's a large chunk, but not everything! Marc had a comment on bluesky regarding this:
> Many SQL aggregations are monotonic operations (e.g. MAX, SUM, etc) that can be partially completed on each node and then post-merged. Some (e.g. DISTINCT) can be transformed into monotonic ops with some effort. Some aren't possible to do this way. (Ref on monotonicity: arxiv.org/pdf/1901.01930)
The benefit of this is that a lot more work is done _close_ to the data. The trend is that bandwidth is getting larger in data centers, but latency isn't improving at the same rate. Reducing the number of round trips between QP and storage greatly improves the overall query latency, even if you have to do more work on the storage.
> Many SQL aggregations are monotonic operations (e.g. MAX, SUM, etc) that can be partially completed on each node and then post-merged. Some (e.g. DISTINCT) can be transformed into monotonic ops with some effort. Some aren't possible to do this way. (Ref on monotonicity: arxiv.org/pdf/1901.01930)
The benefit of this is that a lot more work is done _close_ to the data. The trend is that bandwidth is getting larger in data centers, but latency isn't improving at the same rate. Reducing the number of round trips between QP and storage greatly improves the overall query latency, even if you have to do more work on the storage.