Byte-addressable persistent memory (PM) has been widely studied in the past few years. Recently, the emerging eADR technology further incorporates CPU cache into the persistence domain. The persistent CPU cache is promising to optimize the write performance of PM-based storage systems and facilitate the design of concurrent crash-consistent data structures. In this paper, we propose Spash, a highly scalable persistent hash index for PM systems with persistent CPU cache. Spash fully exploits the benefits of persistent CPU cache to implement a durable linearizable index with low PM access overhead and high concurrency. Spash employs a fine-grained extendible hash architecture and a metadata-free segment design to minimize the number of PM accesses. Moreover, Spash adopts adaptive in-place updates and compacted-flush insertions, which dramatically conserve scarce PM write bandwidth by absorbing a large amount of PM write in the persistent CPU cache. Furthermore, Spash proposes a two-phase concurrency protocol and a collaborative staged doubling mechanism, which leverage the persistent CPU cache and hardware transactional memory to achieve lock-free concurrency and durable linearizability. Spash outperforms the other state-of-the-art persistent hash indexes in YCSB workloads by up to 19.6×.

Persistent memory (PM) promises near-DRAM performance as well as data persistency. Recently, a new feature called eADR is available on the 2 nd generation Intel Optane PM with the 3 rd generation Intel Xeon Scalable Processors. eADR ensures that data stored within the CPU caches will be flushed to PM upon the power failure. Thus, in eADR-enabled PM systems, the globally visible data is considered persistent, and explicit data flushes are no longer necessary. The emergence of eADR presents unique opportunities to build lock-free data structures and unleash the full potential of PM. In this paper, we propose NBTree, a lock-free PM-friendly B + -Tree, to deliver high scalability and low PM overhead. To our knowledge, NBTree is the first persistent index designed for eADR-enabled PM systems. To achieve lock-free, NBTree uses atomic primitives to serialize leaf node operations. Moreover, NBTree proposes four novel techniques to enable lock-free access to the leaf during structural modification operations (SMO), including three-phase SMO, sync-on-write, sync-on-read , and cooperative SMO. For inner node operations, we develop a shift-aware search algorithm to resolve read-write conflicts. To reduce PM overhead, NBTree decouples the leaf nodes into a metadata layer and a key-value layer. The metadata layer is stored in DRAM, along with the inner nodes, to reduce PM accesses. NBTree also adopts log-structured insert and in-place update/delete to improve cache utilization. Our evaluation shows that NBTree achieves up to 11X higher throughput and 43X lower 99% tail latency than state-of-the-art persistent B + -Trees under YCSB workloads.