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Since the 1970s, relational database management systems (RDBMS) have dominated the data landscape. But as businesses collect, store and process more and more data, relational databases are harder and harder to scale.

• At first you might go from a single server to a master/slave setup, and add caching layers in front of the database to relieve load as more and more reads/writes hit the database.
• When performance of queries begins to degrade, usually the first thing to be dropped is indexes,
• followed quickly by denormalization to avoid joins as they become more costly.
• Later you might start to precompute (or materialize) the most costly queries so that queries then effectively become key lookups and perhaps distribute data in huge tables across multiple database shards.

At this point if you step back, many of the key benefits of RDBMSs have been lost —

• referential integrity,
• ACID transactions,
• indexes, and so on.