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# 数据系统 | ||
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## 基石 | ||
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### 可靠性 | ||
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造成错误的原因叫做故障(fault),预料并应对故障的系统特性可称为容错(fault-tolerant)。 | ||
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故障(fault)不同于失效(failure),故障定义的是系统偏离正常状态,失效则是整个系统不能对用户提供服务 | ||
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### 可伸缩性 | ||
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可伸缩性(Scalability) 是用来描述系统应对负载增长能力的术语 | ||
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负载可以用一些称为 负载参数(load parameters) 的数字来描述,如每秒请求数、读写请求比率等等。 | ||
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为了描述性能,单个请求的响应参数是没有太多参考参考价值的,需要通过一个可测量的数值分布来描述: | ||
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![202131141817](/assets/202131141817.png) | ||
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为了明确大多数用户的指标,中位数是最有价值的。 | ||
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为了应对负载,可以进行垂直扩展或者水平扩展。没有一种银弹可以解决所有的应对负载需求,一个良好适配应用的可扩展架构,是围绕着假设(assumption)建立的,这就是所谓负载参数。 | ||
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### 可维护性 | ||
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可操作性:降低运维复杂度。 | ||
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简单性:通过封装降低复杂度。 | ||
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可演化性:简单易懂的系统通常比复杂系统更容易修改。 |