  The explosively growing communication traffic in datacenters imposes
increasingly stringent performance requirements on the underlying networks.
Over the last years, researchers have developed innovative optical switching
technologies that enable reconfigurable datacenter networks (RCDNs) which
support very fast topology reconfigurations. This paper presents D3, a novel
and feasible RDCN architecture that improves throughput and flow completion
time. D3 quickly and jointly adapts its links and packet scheduling toward the
evolving demand, combining both demand-oblivious and demand-aware behaviors
when needed. D3 relies on a decentralized network control plane supporting
greedy, integrated-multihop, IP-based routing, allowing to react, quickly and
locally, to topological changes without overheads. A rack-local synchronization
and transport layer further support fast network adjustments. Moreover, we
argue that D3 can be implemented using the recently proposed Sirius
architecture (SIGCOMM 2020). We report on an extensive empirical evaluation
using packet-level simulations. We find that D3 improves throughput by up to
15% and preserves competitive flow completion times compared to the state of
the art. We further provide an analytical explanation of the superiority of D3,
introducing an extension of the well-known Birkhoff-von Neumann decomposition,
which may be of independent interest.
