November 2020
Beginner to intermediate
214 pages
5h 10m
Chinese
Content preview from 数据库可靠性工程：数据库系统设计与运维指南
Become an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.
16
｜
第
2
章
了解了上述知识后，下面考虑延时
SLO
。如果每分钟都取平均值，那么不管
SLO
是什么，
都不能证明是否实现了目标，因为只是在测量平均值。为什么不让目标更贴近实际情况
呢？可以这样改进
SLO
的定义：在
1
分钟内，对于
99%
的请求，延时必须为
25~100 ms
。
为什么选择
99%
而不是
100%
呢？延时往往呈多峰分布。有正常情况也有异常情况，这是
由复杂的分布式系统中存在的大量偶然性造成的，比如
JVM
（
Java
虚拟机）垃圾收集、数
据库落盘和缓存失效等。因此，我们预估有一定比例的异常值，设定
SLO
旨在识别可容忍
的异常值百分比。
下面考虑负载。我们讨论的是
API
这类简单的响应时间吗？还是测量页面渲染？页面渲染
是一段时间内发生的许多调用的综合。如果要测量页面渲染，我们可能需要将初始响应作
为第一个需求，将最终渲染作为第二个需求，因为二者的间隔时间可能很长。
2.3.2
可用性指标
如前所述，可用性是服务能够在规定时间内响应请求的时间度量，通常用百分比表示。例
如一个系统的可用性是
99.9%
，可以表示为：服务必须在
99.9%
的时间内是可用的。
这允许每年有
526
分钟的故障时间，相当于近
9
小时！要求非常宽松。你可能会问，为什
么不说
100%
？如果你是产品负责人或销售人员，可能会这样做。人们普遍认为，
99%
、
99.9%
和
99.99%
之间分别存在一个数据量的差异，每一次提升都会让系统变得更复杂、更
昂贵，也更容易让工程师分心。另外，如果这是一个通过互联网或远距离传输数据的应用
程序，可以预见传输介质将产生影响，导致系统的可用性无法达到 ...
Become an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
and much more.
Read now
Unlock full access
More than 5,000 organizations count on O’Reilly
O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.