Rethinking Index Design Based on Persistent Memory Device

NVM (non-volatile memory) is a new type of storage medium that has emerged in recent years. On the one hand, similar to DRAM (Dynamic RAM), NVM has low access latency and byte-addressable characteristics; on the other hand, it does not lose data after a power failure. Moreover, it has higher density and lower power consumption. The emergence of NVM provides new opportunities for improving indexing efficiency, and thus many works focus on building NVM-based indexing. However, these works are conducted based on simulated NVM devices. In April 2019, Intel released real NVM hardware AEP (apache pass) based on 3D-XPoint technology. The actual AEP devices are evaluated, and the results show that the write latency of AEP is close to that of DRAM, while the read latency is 3~4 times that of DRAM. Based on actual NVM hardware performance, we find that many past works have biased performance assumptions about NVM, which leaves some past works open to optimizing space. We then revisit previous persistent indexing works. We propose a read-optimized hybrid index (HybridIndex\++) and a hybrid-memory-based asynchronous caching approach for persistent index. Experimental results show that the read performance of HybridIndex\++ is 1.8 times that of existing hybrid index. The asynchronous cache-optimized indexes can reduce latency by up to 50%.