For any Realtime application, we need a Realtime Database. The Firebase Realtime Database is a cloud-hosted NoSQL database that synchronizes the data in Realtime to every connected client. Instead of a typical request-response model, the Firebase database uses the synchronization mechanism that synchronizes the data to all the connected devices within milliseconds. Another key capability is its offline feature. The Firebase SDK persists the data on the disk; so, even if a user loses their internet connection, the app remains responsive. It automatically synchronizes the data once the connection is reestablished. It is supported by iOS, Android, Web, C++, and Unity platforms. We will cover this in detail in the upcoming chapters.

The following screenshot shows the list of features on the left, which are available in Firebase, and we have selected the Realtime Database in the database section. In that section, we have four tabs available:

• DATA
• RULES
• BACKUPS
• USAGE