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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了解应用程序的动态
｜
307
18.1.3
假象
在查找耗时过长的操作时，可能会看到结果中列出的一些长时间运行的内部操作。
MongoDB
可
能会长时间运行若干请求，这取决于你的设置。最常见的是复制线程（它
会尽可能长时间地持续从同步源获取更多操作）和用于分片的回写监听器。任何在
local.
oplog.rs
上长时间运行的请求以及任何
回写监听
命令都可以被忽略。
如果这些操作被终止了，
MongoDB
则会重新启动它们
。然而，通常来说不应该这样做。
终止复制线程会使复制操作短暂地中止，而终止回写监听器可能会导致
mongos
遗漏正常
的写入错误。
18.1.4
防止幻象操作
有一个奇怪的、特定于
MongoDB
的问题有可能会遇到，特别是在将数据批量加载到集合
中时。假设现在有一个任务是在
MongoDB
中进行上千条更新操作
，而
MongoDB
在执行
时一度停滞不前。然后你迅速停止了这个任务并终止了当前正在进行的所有更新。然而，
在终止了旧的更新后，仍然可以看到新的更新继续出现，即使任务已经不再运行。
如果在加载数据时使用了未确认写入的机制，那么应用程序触发写操作的速度可能比
MongoDB
处理它们的速度更快
。如果
MongoDB
中的请求发生了堆积，那么这些写操作
将堆积在操作系统的套接字缓冲区中。当终止
MongoDB
正
在进行的写操作时，就会让
MongoDB
开始处理缓冲区中的写操作
。即使客户端停止发送写操作，
MongoDB
也会处理
那些写入缓冲区的操作，因为它们已经被“接收”了（只是没有被处理）。
防止这些幻像写入的最好方法是执行写入确认机制 ...
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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.