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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深入
MongoDB
｜
387
"genres_1_imdb.rating_1_metacritic_1" : {
...
"uri" : "statistics:table:index-30--2146526997547809066",
...
}
WiredTiger
会将每个集合或索引存储在一个任意大的文件中。影响该文件最大大小的唯一
限制是文件系统中对文件大小的限制。
每当对文档进行更新时，
W
iredTiger
会写入该文档的一个完整的新副本。磁盘上的旧副本
会被标记以供重用，并最终在将来的某个时间点（通常在下一个检查点期间）被覆盖。这
会回收
W
iredTiger
文件中所使用的空间。可以运行
compact
命令将数据移动到文件的前面
位置，在后面留下空闲空间。
W
iredTiger
会定期通过截断文件来删除这些多余的空闲空间。
在压缩过程结束时，多余的空间会返还给文件系统。
B.4
命名空间
每个数据库都是按照命名空间来组织的，这些命名空间会被映射到
WiredTiger
文件。这种
抽象会将存储引擎的内部细节与
MongoDB
的查询层分离开来。
B.5
WiredTiger
存储引擎
WiredTiger
存储引擎是
MongoDB
的默认存储引擎。当服务器启动时，它会打开数据文件
并开始检查点和日志记录过程。它会与操作系统进行配合，操作系统的职责主要是对数据
页进行载入载出，以及将数据刷新到磁盘上。该存储引擎有以下几个重要特性。
•
默认情况下对集合和索引会启用压缩。默认的压缩算法是谷歌的
snappy
。还可以选择
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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.