BPTree: An Optimized Index with Batch Persistence on Optane DC PM

Abstract

Intel Optane DC Persistent Memory (PM) is the first commercially available PM product. Although it meets many hypothesises about PM in previous studies, some other design considerations are observed in subsequent tests. For instance, 1) the internal data access granularity in Optane DC PM is 256B, accesses smaller than 256B will cause read/write amplification; 2) the locking overhead will be amplified when the PM operations are included in the critical area or the lock is added on PM. In this paper, we propose a novel persistent index called BPTree to fit with these new features. The core idea of BPTree is to buffer multiple writes in DRAM first, and later persist them in batches to PM to reduce the write amplification. We add a buffer layer in BPTree to enable the batch persistence, and design a GC-friendly log structure on PM to guarantee the buffer’s durability. To improve the scalability, we also implement a hybrid concurrency control strategy to ensure most of the operations on PM are lock-free, and move the lock from PM to DRAM for the operations that must be locked. Our experiments on Optane DC PM show that BPTree reduces 256B PM writes by a factor of 1.95–2.48x compared to the state-of-the-art persistent indexes. Moreover, BPTree has better scalability in the concurrent environment.