Secondary indices

If range queries can be considered optimal for Cassandra's storage engine, queries based on a secondary index fall at the other end of the spectrum. Secondary indices have been part of Cassandra since the 0.7 release, and they are certainly an alluring feature. In fact, for those who are accustomed to modeling data in relational databases, creating an index is often a go-to strategy to achieve better query performance. However, as with most aspects of the transition to Cassandra, this strategy translates poorly.

To start, let's get familiar with what secondary indices are and how they work. First off, secondary indices are the only type of index that Cassandra will manage for you, so the terms index and secondary index actually refer to the same mechanism. The purpose of an index is to allow query-by-value functionality, which is not supported naturally. This should be a clue as to the potential danger involved in relying on the index functionality.

As an example, suppose...