Storing lots of data as Columns in a Column Family (ref Twissandra)

[Muhammed Nasrullah]

Hello folks,

Twissandra <http://twissandra.com/> (Twitter clone example for Cassandra)
has a public page where every public update/tweet is stored in a column
family under the key !public! like so:

Userline = {
    '!public!': {
        # timestamp of tweet: tweet id
        1267414247561777: '7561a442-24e2-11df-8924-001ff3591711',
        1267414277402340: 'f0c8d718-24e2-11df-8924-001ff3591711',
        1267414305866969: 'f9e6d804-24e2-11df-8924-001ff3591711',
        1267414319522925: '02ccb5ec-24e3-11df-8924-001ff3591711',
    },
}


My question is, because this is the public timeline, it will get a lot of
updates and because this is a single row keyed by '!public!', this won't fit
in memory eventually. Is there a better way to model this? The problem is
that the data needs to be retrieved in reverse chronological order,
something which cannot be done while getting a range of keys without knowing
the start and finish keys in advance.

Thanks!