Foursquare uses MongoDB to power their location-based social network. They have over 9 million users generating around 3 million check-ins per day across over 15 million venues. Foursquare chose MongoDB because it is fast, supports rich queries, sharding, replication, and geo-indexes. Foursquare runs 8 MongoDB clusters across around 40 machines storing over 2.3 billion records and handling around 15,000 queries per second. They developed Rogue, a Scala DSL for MongoDB, to make queries type-safe and add features like pagination, logging, and index awareness.