When B-Tree Meets Skyrmion Memory: How Skyrmion Memory Affects an Indexing Scheme

Because of large cell density, fast read/write performance, and no limited write cycles, magnetic skyrmion racetrack memory (SK-RM) has been regarded as the next-generation main memory technology. However, the characteristics of SK-RM are not friendly for a B+-tree indexing structure that is widely applied to database and file systems because some B+-tree structure's operations (including splitting, merging, and query) need to reproduce skyrmion elements for copying keys and repeatedly shift skyrmion elements to access ports for a binary search operation. In this work, we elaborate on the overheads of establishing a B+-tree structure on the SK-RM architecture. To eliminate the overhead, this work proposes a skyrmion-friendly B+-tree structure, namely Sky-tree, that fully exploits the benefits of the SK-RM architecture by a bit-level binary search method, node-based skyrmion recycler, and an intratrack node splitting strategy. The design principle of the skyrmion-friendly B+-tree is to minimize the number of generated skyrmion elements and the shift overhead per query operation. The experimental results show that our skyrmion-friendly B+-tree structure can improve the performance by up to 78%, compared with a baseline solution.