Ah, I see. This is a known problem with the performance of the protobuf serialization library we're using in the Ruby driver (see https://github.com/rethinkdb/rethinkdb/issues/897). It bottlenecks the CPU and should be fixed in the next release.
In the meantime, you could try running a multithreaded/multiprocess script -- that would significantly increase throughput.
In the meantime, you could try running a multithreaded/multiprocess script -- that would significantly increase throughput.
Sorry you ran into this -- it'll be fixed ASAP.