系统负载 是描述系统繁忙程度的指标，一般通过数个 负载参数（load parameter）描述。
- API 服务器：每秒请求数（QPS）
系统可能关心 平均负载（load average），也可能关心极端场景，取决于业务场景。
Load can be described with a few numbers which we call load parameters. The best choice of parameters depends on the architecture of your system: it may be requests per second to a web server, the ratio of reads to writes in a database, the number of simultaneously active users in a chat room, the hit rate on a cache, or something else. Perhaps the average case is what matters for you, or perhaps your bottleneck is dominated by a small number of extreme cases.
The system load is a measure of the amount of computational work that a computer system performs.
Martin Kleppmann, Designing Data-Intensive Applications, n.d. p11 ↩︎