Description

Velox is initially designed to use multiple threads in each context. To fit spark's working model, we limit 1 thread per context. It's needed by fallback.

Since Velox backend can fully offload lots of queries, it will be interesting to investigate multiple threads per context. We can set task.cores to more than 1 then set to Velox's backend threads. Then use larger partition and see how the performance looks like.

@zhztheplayer Is there any specific consideration on memory management side?