In Cassandra terminology, what is TimeUUID?

Question

In Cassandra terminology, what is TimeUUID and when is it used?

Answer 1

TimeUUID is a random global unique identifier. 16 bytes.

Sample hex presentation: a4a70900-24e1-11df-8924-001ff3591711

See http://en.wikipedia.org/wiki/Universally_Unique_Identifier

It may serve as a primary key in terms of relational database or when you need to store a list of values under some key.

For example check this open source twitter example based on cassandra:

http://twissandra.com/

http://github.com/ericflo/twissandra

User = {
    'a4a70900-24e1-11df-8924-001ff3591711': {
        'id': 'a4a70900-24e1-11df-8924-001ff3591711',
        'username': 'ericflo',
        'password': '****',
    },
}

Username = {
    'ericflo': {
        'id': 'a4a70900-24e1-11df-8924-001ff3591711',
    },
}

Friends = {
    'a4a70900-24e1-11df-8924-001ff3591711': {
        # friend id: timestamp of when the friendship was added
        '10cf667c-24e2-11df-8924-001ff3591711': '1267413962580791',
        '343d5db2-24e2-11df-8924-001ff3591711': '1267413990076949',
        '3f22b5f6-24e2-11df-8924-001ff3591711': '1267414008133277',
    },
}

Here user is assigned a unique key a4a70900-24e1-11df-8924-001ff3591711 which is used to refer to the user from other places.