Persistent memory (PM) provides large-scale non-volatile memory (NVM) with DRAM-comparable performance. The non-volatility and other unique characteristics of PM architecture bring new opportunities and challenges for the efficient storage system design. For example, some recent crash-consistent and write-friendly hashing schemes are proposed to provide fast queries for PM systems. However, existing PM hashing indexes suffer from the concurrency bottleneck due to the blocking resizing and expensive lock-based concurrency control for queries. Moreover, the lack of PM awareness and systematical design further increases the query latency. To address the concurrency bottleneck of lock contention in PM hashing, we propose clevel hashing, a lock-free concurrent level hashing scheme that provides non-blocking resizing via background threads and lock-free search/insertion/update/deletion using atomic primitives to enable high concurrency for PM hashing. By exploiting the PM characteristics, we present a holistic approach to building clevel hashing for high throughput and low tail latency via the PM-aware index/allocator co-design. The proposed volatile announcement array with a helping mechanism coordinates lock-free insertions and guarantees a strong consistency model. Our experiments using real-world YCSB workloads on Intel Optane DC PMM show that clevel hashing, respectively, achieves up to 5.7× and 1.6× higher throughput than state-of-the-art P-CLHT and Dash while guaranteeing low tail latency, e.g., 1.9×–7.2× speedup for the p99 latency with the insert-only workload.

Due to the salient DRAM-comparable performance, TB-scale capacity, and non-volatility, persistent memory (PM) provides new opportunities for large-scale in-memory computing with instant crash recovery. However, programming PM systems is error-prone due to the existence of crash-consistency bugs, which are challenging to diagnose especially with concurrent programming widely adopted in PM applications to exploit hardware parallelism. Existing bug detection tools for DRAM-based concurrency issues cannot detect PM crash-consistency bugs because they are oblivious to PM operations and PM consistency. On the other hand, existing PM-specific debugging tools only focus on sequential PM programs and cannot effectively detect crash-consistency issues hidden in concurrent executions.