November 2021
Intermediate to advanced
410 pages
12h 1m
Chinese
Content preview from MongoDB权威指南（第3版）
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352
｜
第
22
章
而引发连锁反应。通常存在一个临界点，超出临界点后磁盘性能便会迅速下降。因此，应
该尽量避免磁盘在其最大负载下运转。
应该不断跟踪缺页错误的数量。如果在缺页错误达到某一数量时应用程序运
行良好，那么就有了一个系统可以处理多少缺页错误的基线。如果随着缺页
错误的上升性能开始下降，那么就有了一个应该发出告警的阈值。
通过查看
serverStatus
输出中的
"page_faults"
字段，可以看到每个数据库的缺页错误
统计：
> db.adminCommand({"serverStatus": 1})["extra_info"]
{ "note" : "fields vary by platform", "page_faults" : 50 }
其中
"page_faults"
表示
MongoDB
必须去磁盘读取数据的次数（自启动以来）。
22.1.4
I/O
等待
缺页错误通常与
CPU
空闲等待磁盘响应（称为
I/O
等待）的时间密切相关。一些
I/O
等待
是正常的，
MongoDB
有时不得不去磁盘读取数据
，并且无法完全避免对其他操作的妨碍。
重要的是，要确保
I/O
等待不会持续增加或者接近
100%
。从图
22-4
中可以看出
，
I/O
等待
处于
100%
左右，这表明磁盘正在超载。
CPU 时间
图 22-4：I/O 等待处于 100% 左右
22.2
计算工作集的大小
通常来说，内存中的数据越多，
MongoDB
的运行速度就越快。因此，按照从最快到最慢
的顺序，应用程序可能有以下几种情况。
1.
整个数据集都在内存中
。这是非常好的，但通常代价过大或不可行。对于某些依赖于快 ...
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