TIME COMPLEXITY: O(1) to set every key
DESCRIPTION:
Set the the respective keys to the respective values. MSET will replace old values with new values, while MSETNX will not perform any operation at all even if just a single key already exists.
Because of this semantic MSETNX can be used in order to set different keys representing different fields of an unique logic object in a way that ensures that either all the fields or none at all are set.
Both MSET and MSETNX are atomic operations. This means that for instance if the keys A and B are modified, another client talking to Redis can either see the changes to both A and B at once, or no modification at all.
RETURN VALUE: Status code reply Basically +OK as MSET can't fail