HATree: A Hotness-Aware Tree Index with In-Node Hotspot Cache for NVM/DRAM-Based Hybrid Memory Architecture

Abstract

The emerging of Non-Volatile Memory (NVM) has changed the traditional DRAM-only memory system. Compared to DRAM, NVM has the advantages of non-volatility and large capacity. However, as the read/write speed of NVM is still lower than that of DRAM, building DRAM/NVM-based hybrid memory systems is a feasible way of adding NVM into the current computer architecture. This paper aims to optimize the well-known B${^+}$-tree for hybrid memory. We present a new index called HATree (Hotness-Aware Tree) that can identify and maintain hot keys with an in-node hotspot cache. The novel idea of HATree is using the unused space of the parent of leaf nodes (PLNs) as the hotspot data cache. Thus, no extra space is needed, but the in-node hotspot cache can efficiently improve query performance. We present the new node structures and operations of HATree and conduct experiments on synthetic workloads using real Intel Optane DC Persistent Memory. The comparative results with three existing state-of-the-art indices, including FPTree, LBTree, and BaseTree, suggest the efficiency of HATree.