In the past decade, cloud databases have experienced rapid development and growth. PolarDB, Alibaba's cloud-native OLTP database, has evolved significantly to meet the increasing demand for cloud-native architectures and now serves hundreds of thousands of customers across various industries. This paper presents PolarDB's evolution over the past eight years, with a focus on scalability, performance, and cost-efficiency. Initially, PolarDB adopted a primary-replica architecture based on disaggregated storage, with an emphasis on enhancing single-node performance for scale-up in modern many-core systems. To achieve this, we co-designed PolarDB with cutting-edge hardware, including RDMA, to improve performance. Meanwhile, we refined the internal architecture, including improvements to B+ tree concurrency control and transaction management, ensuring high scalability in scale-up scenarios. More recently, our focus has shifted to scaling out PolarDB to meet the performance and scalability needs of ultra-large-scale applications. By leveraging RDMA, we optimized distributed transaction processing, transforming PolarDB into a high-performance, high-scalability and cost-effective distributed database. In the TPC-C benchmark, PolarDB scaled out to 2340 nodes and achieved over 2 billion tpmC, with a jitter rate of no more than 0.16% during the 8-hour stress test. Compared to the second- and third-highest-performing databases in public TPC-C results, PolarDB's tpmC is 2.52× and 2.91× higher, respectively. In terms of cost-effectiveness, PolarDB's per-tpmC cost is 37% and 79.5% lower than that of the other two systems, respectively.

Modern data-centric applications frequently need to store and read data with low latency. These requirements are difficult to achieve, even on high performance processors paired with fast solid state drives (SSDs). To this end, LSM tree is widely used in many systems such as in RocksDB and considered as an ideal index structure that fits SSDs. However, in spite of many improvements to LSM tree over the years, fundamental problems of limited read performance and expensive compaction operations remain. Microsoft Research proposed Bw-tree, a variant of B+ tree layered on top of log structured storage. Bw-tree achieves fast ingestion of data, similar to LSM tree, meanwhile it has less drawback on read performance and compaction. However, except for Microsoft, the industrial strength implementation of Bw-tree is rare. The open source OpenBw-Tree from Carnegie Mellon University was designed only for main memory. This paper describes Bwe-tree, an implementation and a significant evolution of Bw-tree on fast storage. It makes two contributions. First, Bwe-tree addresses reliability and performance issues revealed during running Bw-tree on fast storage in production, by revising structural modification operations, introducing page concurrency control, and storing large-size values off-tree. Performance improvements over Bw-tree are verified by experiments. Second, it demonstrates that Bw-tree is an effective alternative tree structure on SSDs. Compared to RocksDB (LSM tree) and BerkeleyDB (B+ tree), Bwe-vtree performs dramatically better (up to 3X or more) for the YCSB workloads. Our Bwe-vtree implementation has been integrated into production systems in Alibaba, including a flagshin cloud-native database service.

The increasing interest that has been drawn to LTE system used in High-Speed Railway therefore requires measurement and analysis of broadband mobile channel for train-ground communications. By the approval of the Ministry of Railways of China, extensive and practical measurements are performed on Harbin- Dalian passenger dedicated line with the maximum running speed of 370 km/h. Based on the hierarchical two-hop network structure, this paper first presents comprehensive analyzed results of channel characteristics in viaduct scenario, including both the large-scale and small-scale fading parameters. The proposed path loss model benefits LTE system link budget and feasible transceiver-range determination. In particular, channel impulse response, power delay profile, the delay spread, the number of paths and delay-Doppler spectrum are extracted, evaluated and reported. All these informative results promote the evaluation and verification of broadband communication system on High-Speed Railway.

The increasing interest that has been drawn to the LTE system used in High-Speed Railway therefore requires measurements and analysis of wideband mobile channel for train-ground communications. Based on the hierarchical two-hop network structure, extensive and practical measurements are performed on Harbin-Dalian passenger dedicated line with a speed up to 370 km/h by the approval of the Ministry of Railways of China. This paper first presents comprehensive analyzed results of the statistical channel properties, including both the large-scale and small-scale fading parameters. The proposed path loss model is applicable to high-speed railway plain scenarios and benefits the link budget of the LTE system. In particular, channel impulse response, power delay profile, the delay spread, the number of paths and delay-Doppler spectrum are extracted, evaluated and reported. All these results promote the evaluation and verification of wireless wideband communications on the high-peed railway.