As there are two ways to support wide rows in CQL3..One is to use composite keys and another is to use collections like Map, List and Set. The composite keys method can have
Apart from the performance issue, there is a protocol issue which limits the number of items you can access to 65536.
http://mail-archives.apache.org/mod_mbox/cassandra-user/201305.mbox/%3CCAENxBwx6pcSA=cWn=dKW_52K5odw5F3Xigj-zn_4BwFth+4ruA@mail.gmail.com%3E