Zen+: a robust NUMA-aware OLTP engine optimized for non-volatile main memory

Emerging non-volatile memory (NVM) technologies like 3DXpoint promise significant performance potential for OLTP databases. However, transactional databases need to be redesigned because the key assumptions that non-volatile storage is orders of magnitude slower than DRAM and only supports blocked-oriented accesses have changed. NVMs are byte-addressable and almost as fast as DRAM. The capacity of NVM is much (4-16x) larger than DRAM. Such NVM characteristics make it possible to build OLTP databases entirely in NVM main memory. This paper studies the structure of OLTP engines with hybrid NVM and DRAM memory. We observe three challenges to design an OLTP engine for NVM: tuple metadata modifications, NVM write redundancy, and NVM space management. We propose Zen, a high-throughput log-free OLTP engine for NVM. Zen addresses the three design challenges with three novel techniques: metadata-enhanced tuple cache, log-free persistent transactions, and light-weight NVM space management. We further propose Zen+ by extending Zen with two mechanisms, i.e., MVCC-based adaptive execution and NUMA-aware soft partition, to robustly and effectively support long-running transactions and NUMA architectures. Experimental results on a real machine equipped with Intel Optane DC Persistent Memory show that compared with existing solutions that run an OLTP database as large as the size of NVM, Zen achieves 1.0x-10.1x improvement while attaining fast failure recovery, and supports ten types of concurrency control methods. Experiments also demonstrate that Zen+ robustly supports long-running transactions and efficiently exploits NUMA architectures.