Decrements the value associated with the key by 1 or as specified by dec_by.
The key that was used to store the variable in the cache. key is case sensitive.
The value by which the variable associated with the key will get decremented. If the argument is a floating point number it will be truncated to nearest integer. The variable associated with the key should be of type long, otherwise the function fails and returns false.
Will be set to true on success and false on failure.
Returns the decremented value on success and false on failure.