mongodb 怎么合并多个 database

Question

现在一个实例里有 DBA, DBB, DBC, NewDB，如何把ABC导入到NewDB？
结构是一样的，试过For Insert 和 InsertMany，但是数据有接近500W，插了没几条就不工作了。而且效率太低。
请问有什么高效的办法吗？

Answer 1

如果是复制集的话倒是有办法，不是十分直观不过我们有renameCollection Command:
注意：务必读完上面的链接再动手。

{ renameCollection: "<source_namespace>", to: "<target_namespace>", dropTarget: <true|false> }

Field	Type	Description
renameCollection	string	The namespace of the collection to rename. The namespace is a combination of the database name and the name of the collection.
to	string	The new namespace of the collection. If the new namespace specifies a different database, the renameCollection command copies the collection to the new database and drops the source collection.
dropTarget	boolean	Optional. If true, mongod will drop the target of renameCollection prior to renaming the collection. The default value is false.

Example:

use admin
db.runCommand( { renameCollection: "DBA.xxx", to: "NewDB.xxx" } )
db.runCommand( { renameCollection: "DBA.yyy", to: "NewDB.yyy" } )
...