Realm

Realm is a mobile-first object database developed by MongoDB, designed specifically for iOS and Android applications requiring fast local data storage and cloud synchronization. Unlike traditional databases that use SQL or document models, Realm stores data as native objects that developers interact with directly in Swift, Kotlin, or Java—eliminating the need for ORMs or serialization layers. This object-oriented approach significantly reduces code complexity and improves performance, with queries executing up to 10x faster than SQLite for common mobile operations.

Realm’s architecture prioritizes mobile performance through zero-copy architecture and lazy loading, keeping memory footprint minimal even with large datasets. The database runs entirely on-device, providing instant data access without network latency, while optional Realm Sync enables automatic cloud synchronization with MongoDB Atlas. This hybrid approach gives mobile apps offline-first capabilities with seamless online sync—changes made offline automatically merge when connectivity returns, with built-in conflict resolution handling complex scenarios.

Mobile developers choose Realm for its reactive architecture that automatically updates UI components when underlying data changes, eliminating manual refresh logic. The database supports advanced features like encryption, migration helpers, and cross-platform data sharing between iOS and Android. Realm’s free tier and flexible pricing make it accessible for indie developers, while enterprise features like event handling and custom conflict resolution support large-scale applications. Integration with MongoDB’s cloud ecosystem provides powerful backend capabilities without managing separate database infrastructure.