MongoDB's Touch Command
Here's a quick tip from the official MongoDB blog. In MongoDB 2.2, the 10gen team added a touch command that loads data from the data storage layer into memory. . .
The touch command will load a collection’s documents, indexes or both into memory. This can be ideal to preheat a newly started server, in order to avoid page faults and slow performance once the server is brought into production. You can also use this when adding a new secondary to an existing replica set to ensure speedy subsequent reads.
Read the full post here: