touch

2.2 新版功能.

The touch command loads data from the data storage layer into memory. touch can load the data (i.e. documents,) indexes or both documents and indexes. Use this command to ensure that a collection, and/or its indexes, are in memory before another operation. By loading the collection or indexes into memory, mongod will ideally be able to perform subsequent operations more efficiently. The touch command has the following prototypical form:

{ touch: [collection], data: [boolean], index: [boolean] }

By default, data and index are false, and touch will perform no operation. For example, to load both the data and the index for a collection named records, you would use the following command in the mongo shell:

db.runCommand({ touch: "records", data: true, index: true })

touch will not block read and write operations on a mongod, and can run on secondary members of replica sets.