Shared-nothing, distributed databases scale transactional and analytical processing over a large data volume by spreading data across servers. However, static sharding of data across nodes makes such systems fail to timely adapt to changing workloads and struggle to obey the cloud pay-as-you-go model. Migrating shards between nodes online is a key technique to react to dynamic changes of workloads for cloud elasticity. Existing approaches introduce severely degraded performance and service interruption, resulting in SLA violation on the cloud; or they are tailor-made to deterministic databases. In this paper, we propose Remus, a new live migration approach for shared-nothing, distributed databases with snapshot isolation. Remus migrates shards between nodes with zero service interruption and minimal performance impact. This is achieved by an efficient unidirectional dual execution during migration. We implement Remus on a shared-nothing, distributed version of PolarDB-PG and evaluate it against state-of-the-art approaches using standard OLTP workloads TPC-C and YCSB, and hybrid workloads consisting of long-lived and short transactions. The results demonstrate Remus is the only effective approach to achieve the goal of zero transaction interruption, zero downtime and marginal performance impact, paving the way for applying the shared-nothing architecture to a cloud database which needs to provide elasticity while guaranteeing strict SLAs.

Recently, the trend of developing digital twins for smart cities has driven a need for managing large-scale multidimensional, dynamic, and scene-oriented spatial data. Due to larger data scale and more complex data structure, queries over such data are more complicated and expensive than those on traditional spatial data, which poses challenges to the system efficiency and deployment costs. The existing spatial databases have limited support in both data types and operations. Therefore, a new-generation spatial database with excellent performance and effective deployment costs is needed. This paper presents Ganos, a cloud-native spatial database engine of PolarDB for PostgreSQL that is developed by Alibaba Cloud, to efficiently manage multidimensional, dynamic, and scene-oriented spatial data. Ganos models 3D space and spatio-temporal dynamics as first-class citizens. Also, it natively supports spatial/spatio-temporal data types such as 3DMesh, Trajectory, Raster, PointCloud, etc. Besides, it implements a novel extended-storage mechanism that utilizes cloud-native object storage to reduce storage costs and enable uniform operations on the data in different storages. To facilitate processing "big" queries, Ganos extends PolarDB and provides spatial-oriented multi-level parallelism under the architecture of decoupling compute from storage in cloud-native databases, which achieves elasticity and excellent query performance. We demonstrate Ganos in real-life case studies. The performance of Ganos is evaluated using real datasets, and promising results are obtained. Finally, based on the extensive deployment and application of Ganos, the lessons learned from our customers and the expectations of modern cloud applications for new spatial database features are discussed.

\beginabstract The trend in the DBMS market is to migrate to the cloud for elasticity, high availability, and lower costs. The traditional, monolithic database architecture is difficult to meet these requirements. With the development of high-speed network and new memory technologies, disaggregated data center has become a reality: it decouples various components from monolithic servers into separated resource pools (e.g., compute, memory, and storage) and connects them through a high-speed network. The next generation cloud native databases should be designed for disaggregated data centers. In this paper, we describe the novel architecture of \name, which follows thedisaggregation design paradigm: the CPU resource on compute nodes is decoupled from remote memory pool and storage pool. Each resource pool grows or shrinks independently, providing \revon-demand provisoning at multiple dimensions while improving reliability. We also design our system to mitigate the inherent penalty brought by resource disaggregation, and introduce optimizations such as optimistic locking and index awared prefetching. Compared to the architecture that uses local resources, \name achieves better dynamic resource provisioning capabilities and 5.3 times faster failure recovery speed, while achieving comparable performance. \endabstract