Sorting on Byte-Addressable Storage: The Resurgence of Tree Structure

Abstract

The tree structure is notably popular for storage and indexing; however, tree-based sorting such as tree sort is rarely used in practice. Nevertheless, with the advent of byte-addressable storage (BAS), the tree structure captures our attention with its write-once property. This property aligns well with BAS's asymmetric read-write characteristics. In this paper, we seek to answer the question: Can tree-based sorting algorithms outperform existing algorithms in the hybrid DRAM-BAS system? To address this, first, we conduct a comprehensive study to assess the compatibility of existing sorting algorithms with such hybrid memory systems and explore the challenges. We then delve into various design dimensions of tree-sort algorithms which leads to an optimized variant, TSort. Finally, a comparative analysis is conducted among three different sets of sorting algorithms, including in-place sorts, external sorts, and tree-based sorts. The results indicate that TSort not only challenges the traditional negative perceptions of the tree structure in sorting but also exhibits excellent performance. It outperforms all other counterparts across diverse datasets, whether uniformly distributed or skewed, in most cases.