We have built openGauss, an enterprise-grade open-source database system. openGauss has fulfilled its design goal of high performance, high availability, high security, and high intelligence. For high performance, it leverages NUMA (non-uniform memory access)-aware data access among multiple cores to enable efficient concurrent transaction processing, and symmetric multi-processing to make use of parallel processing resources adaptively. Moreover, memory-optimized tables (MOTs) are designed to put everything in memory. For high availability, a three-tier pooling architecture that shares storage among the master and standby instances is proposed to achieve availability at 99.99%, containing both a distributed memory service (DMS) and a distributed storage service (DSS). For high security, it is a fully encrypted database with safe storage features, efficient complex querying, and tamper-proof. For high intelligence, an AI-based optimizer in the kernel and a self-driving platform named DBMind are demonstrated to achieve better performance and greater user-friendliness. openGauss has served over 150 enterprises and institutions since its release in 2020. We share the lessons we learned from its development and operation, and our customers.