The data dictionary in Cassandra 1.2

The system keyspace in Cassandra 1.2 contains tables with information about the cluster and its nodes, including gossip data, tokens for virtual nodes, batch logs, hinted handoffs, index creation status, node IDs, range transfer status, and request traces. These tables correspond to CREATE TABLE syntax and provide drivers with necessary introspection without relying on old Thrift calls. However, users should be cautious when updating data in the system keyspace as schema changes are not allowed.