Redis can be told that a key should only exist for a certain length of time. This is accomplished with the EXPIRE and TTL commands.


    SET resource:lock "Redis Demo"
    EXPIRE resource:lock 120
This causes the key resource:lock to be deleted in 120 seconds. You can test how long a key will exist with the TTL command. It returns the number of seconds until it will be deleted.


    TTL resource:lock => 113
    // after 113s
    TTL resource:lock => -2
The -2 for the TTL of the key means that the key does not exist (anymore). A -1 for the TTL of the key means that it will never expire. Note that if you SET a key, its TTL will be reset.


    SET resource:lock "Redis Demo 1"
    EXPIRE resource:lock 120
    TTL resource:lock => 119
    SET resource:lock "Redis Demo 2"
    TTL resource:lock => -1