* Experiment with multi-threaded backend better I/O utilization

  This would allow a single query to make use of multiple I/O channels
  simultaneously.  One idea is to create a background reader that can
  pre-fetch sequential and index scan pages needed by other backends.
  This could be expanded to allow concurrent reads from multiple devices
  in a partitioned table.

* Experiment with multi-threaded backend better CPU utilization

  This would allow several CPUs to be used for a single query, such as
  for sorting or query execution.