决定使用一个数据库（Database Software）时我们在考虑什么？
https://dev.mysql.com/doc/refman/8.0/en/innodb-architecture.html
Database scalability has three basic dimensions: amount of data, volume of requests and size of requests. Requests come in many sizes: transactions generally affect small amounts of data, but may approach thousands per second; analytic queries are generally fewer, but may access more data. A related concept is elasticity, the ability of a system to transparently add and subtract capacity to meet changing workloads.[10]
Vertical database scaling implies that the database system can fully exploit maximally configured systems, including typically multiprocessors with large memories and vast storage capacity. Such systems are relatively simple to administer, but may offer reduced availability. However, any single computer has a maximum configuration. If workloads expand beyond that limit, the choices are either to migrate to a different, still larger system, or to rearchitect the system to achieve horizontal scalability.[10]
Horizontal database scaling involves adding more servers to work on a single workload. Most horizontally scalable systems come with functionality compromises. If an application requires more functionality, migration to a vertically scaled system may be preferable.[10]