Crash recoverable ARMv8-oriented B+-tree for byte-addressable persistent memory

The byte-addressable non-volatile memory (NVM) promises persistent memory. Concretely, ARM processors have incorporated architectural supports to utilize NVM. In this paper, we consider tailoring the important B+-tree for NVM operated by a 64-bit ARMv8 processor. We first conduct an empirical study of performance overheads in writing and reading data for a B+-tree with an ARMv8 processor, including the time cost of cache line flushes and memory fences for crash consistency as well as the execution time of binary search compared to that of linear search. We hence identify the key weaknesses in the design of B+-tree with ARMv8 architecture. Accordingly, we develop a new B+-tree variant, namely, crash recoverable ARMv8-oriented B+-tree (Crab-tree). To insert and delete data at runtime, Crab-tree selectively chooses one of two strategies, i.e., copy on write and shifting in place, depending on which one causes less consistency cost to performance. Crab-tree regulates a strict execution order in both strategies and recovers the tree structure in case of crashes. We have evaluated Crab-tree in Raspberry Pi 3 Model B+ with emulated NVM. Experiments show that Crab-tree significantly outperforms state-of-the-art B+-trees designed for persistent memory by up to 2.6x and 3.2x in write and read performances, respectively, with both consistency and scalability achieved.