Memory-based storage currently offers the highest-performance distributed storage, keeping the primary copy of all data in DRAM. Recent advances in non-volatile main memory (NVMM) technologies promise latency similar to DRAM at reduced cost and energy, but will make providing high availability more challenging. Previous approaches to failure recovery involve maintaining multiple identical replicas or relying on fast offline restoration of data from backup replicas stored on SSD. Unfortunately, NVMM's combination of lower write throughput and increased storage density means that offline restoration can no longer provide sufficiently fast recovery, and maintaining multiple identical replicas is generally cost prohibitive.

Duty-cycling is generally adopted in existing sensor networks to reduce power consumption and these networks depend on neighbor discovery protocols to ensure that nodes wake up and discover each other. For different neighbor discovery protocols, the discovery latency is determined by two factors: the wake-sleep pattern and slot size. To the best of our knowledge, previous works on neighbor discovery have thus far been focused on improving the wake-sleep pattern. In this paper, we investigate the extent to which we can improve discovery latency by reducing the slot size. We found that by reducing the slot size, i.e., reducing the listening time in active slots, the collisions between beacons and synchronization between nodes become more severe, which can lead to discovery failures that are not predicted by existing theoretical models. We show that we can mitigate these effects by reducing the number of beacons and introducing randomization. We propose a new continuous-listening-based neighbor discovery algorithm called Spotlight. Our evaluations with a practical sensor testbed suggest that Spotlight can achieve a 50% reduction in discovery latency over existing state-of-the-art neighbor discovery protocols without increasing power consumption in existing sensor networks.