MongoDB 2.2 introduced the
touch command, which 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.
I could see how this command could be useful for a caching system, but I haven’t seen it in any database. It’s probably a workaround for the memory mapped files mechanism used by MongoDB’s persistence.
Original title and link: MongoDB Touch Command ( ©myNoSQL)