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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366
｜
第
23
章
2.
管理唯一索引带来的混乱
在任何集合中如果存在唯一索引（除了
"_id"
之外），则应该考虑使用
mongodump
和
mongorestore
之外的备份方式
。唯一索引要求数据在复制期间不会以违反唯一约束的方式
进行更改。确保这一点最安全的方法是先“冻结”数据，然后按照前面介绍过的方法进行
备份。
如果决定使用
mongodump
和
mongorestore
，那么在从备份恢复时可能需要对数据进行预处
理。
23.3
副本集的特殊注意事项
在备份副本集时，除了所需数据之外，还需要获取副本集的状态，以确保生成整个部署集
群的准确时间点快照。
通常，应该对从节点进行备份：这可以减轻主节点的负载，并且锁定从节点不会影响应用
程序（只要应用程序不向从节点发送读请求）。可以使用前面介绍的
3
种方法中的任何一
种来备份副本集成员，但是建议使用文件系统快照或复制数据文件的方式。这两种技术在
应用到副本集从节点上时不需要做任何修改。
当启用了复制时，
mongodump
的使用就不那么简单了
。首先，如果使用了
mongodump
，
则必须使用
--oplog
选项进行备份，以获得某个时间点的快照，否则备份的状态会与集群
中任何其他成员的状态都不匹配。在从
mongodump
备份恢复时
，还必须创建一份
oplog
，
否则被恢复的成员就不知道它被同步到哪里了。
要从
mongodump
备份恢复副本集成员
，需要将目标副本集成员作为单机服务器启动，该
服务器上要有一个空的数据目录，并使用
--oplogReplay
选项在其上运行
mongorestore ...
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