In-memory learned index has been an efficient approach supporting in-memory fast data access. However, existing learned indexes are inefficient in supporting variable-length keys. To address this issue, we propose a new in-memory learned index called LIVAK that adopts a hybrid structure involving trie, learned index, and B+-tree. Each node indexes an 8-byte slice of keys, and we use learned indexes for large nodes but B+-trees for small nodes. Also, LIVAK presents a character re-encoding mechanism to avoid performance degradation. We compare LIVAK with B+-tree, Masstree, and SIndex on various datasets and workloads, and the results suggest the efficiency of LIVAK.

Non-Volatile Memory (NVM) has emerged as an alternative to next-generation main memories. Although many tree indices have been proposed for NVM, they generally use B+-tree-like structures. To further improve the performance of NVM-aware indices, we consider integrating learned indexes into NVM. The challenges of such an integration are two fold: (1) existing NVM indices rely on small nodes to accelerate insertions with crash consistency, but learned indices use huge nodes to obtain a flat structure. (2) the node structure of learned indices is not NVM friendly, meaning that accessing a learned node will cause multiple NVM block misses. Thus, in this paper, we propose a new persistent learned index called PLIN. The novelty of PLIN lies in four aspects: an NVM-aware data placement strategy, locally unordered and globally ordered leaf nodes, a model copy mechanism, and a hierarchical insertion strategy. In addition, PLIN is proposed for the NVM-only architecture, which can support instant recovery. We also present optimistic concurrency control and fine-grained locking mechanisms to make PLIN scalable to concurrent requests. We conduct experiments on real persistent memory with various workloads and compare PLIN with APEX, PACtree, ROART, TLBtree, and Fast&Fair. The results show that PLIN achieves 2.08x higher insertion performance and 4.42x higher query performance than its competitors on average. Meanwhile, PLIN only needs ~30 μs to recover from a system crash.

The advance of byte-addressable persistent memory (PM) makes it a hot topic to revisit traditional tree indices such as B+-tree and radix tree, and a few new persistent memory-friendly tree indices have been proposed. However, due to the special features of persistent memory compared to DRAM and the limitations of B+-tree-like indices, it is much harder to optimize both search and write performance for tree indices on persistent memory. As a result, most existing indices for persistent memory, e.g., WB-tree, proposed to improve write performance while sacrificing search performance. Aiming to optimize both write and search performance for tree indices on persistent memory, in this paper, we first propose a novel Two-Layer Architecture (TLA) for constructing tree indices on persistent memory. The key idea, of TLA is to organize the index with a search-optimized top layer and a write-optimized bottom layer, letting the top layer optimize search performance and the bottom layer improve write performance. By adopting efficient structures for the two layers, TLA can boost both write and search performance for tree indices on persistent memory. Following the TLA architecture, we present a new index called TLBtree (Two-Layer B+-tree) offering high search and write performance for persistent memory. Moreover, we develop a concurrent TLBtree to support non-blocking read operations in multi-core environment. We evaluate our proposals under a server equipped with real Intel Optane persistent memory. The results show that TLBtree outperforms the state-of-the-art tree indices, including WB-tree, Fast&Fair, and FPTree, in both search and write performance. Also, the concurrent TLBtree can achieve up to 3.7x speedup than its competitors under the multi-core environment.

With the development of networked radars and wireless communication technologies, electromagnetic data is becoming a new type of big data.Compared with other kinds of big data, such as Internet big data, financial big data, and healthcare big data, electromagnetic big data has some special properties.For example, they usually contain rich and varying labels that describe the features of electromagnetic space.However, existing big-data benchmark tools cannot support the generation and test of electromagnetic big data.In this paper, we aim at providing a simulation-based testbed for electromagnetic big data.The testbed, named STEM, can simulate real-world electromagnetic big data.It supports generating real-time electromagnetic data streams with varying labels.In addition, it is reusable, reconfigurable, and flexible for users to generate workloads for different scenarios.After a brief introduction on the architecture of STEM, we present the implemental details of STEM.Then, we present a case study as well as performance evaluation to demonstrate the usability and flexibility of STEM.