On 8th of September, Alvaro Herrera committed patch:
Allow per-tablespace effective_io_concurrency Per discussion, nowadays it is possible to have tablespaces that have wildly different I/O characteristics from others. Setting different effective_io_concurrency parameters for those has been measured to improve performance. Author: Julien Rouhaud Reviewed by: Andres Freund
Continue reading Waiting for 9.6 – Allow per-tablespace effective_io_concurrency