Yes, this is what I am worrying about.

2011/8/24 Ryan King <ryan@twitter.com>
On Tue, Aug 23, 2011 at 10:03 AM, Alvin UW <alvinuw@gmail.com> wrote:
> Hello,
>
> As mentioned by Ed Anuff in his blog and slides, one way to build customized
> secondary index is:
> We use one CF, each row to represent a secondary index, with the secondary
> index name as row key.
> For example,
>
> Indexes = {
> "User_Keys_By_Last_Name" : {
> "adams" : "e5d61f2b-",
> "alden" : "e80a17ba-",
> "anderson" : "e5d61f2b-",
> "davis" : "e719962b-",
> "doe" : "e78ece0f-",
> "franks" : "e66afd40-",
> : ,
> }
> }
>
> But the whole secondary index is partitioned into a single node, because of
> the row key.
> All the queries against this secondary index will go to this node. Of
> course, there are some replica nodes.
>
> Do you think this is a scalability problem, or any better solution to solve
> it?

Its certainly a scalability problem in that this solution has a hard
ceiling (this index can't get larger than the capacity of any single
node). It will probably work on small datasets, but if your dataset is
small then why are you using cassandra?

-ryan