Modern online games need to store huge amounts of data: player accounts, inventory, currencies, stats, world progress, guild data, match results, analytics—the list is endless.
Unlike single-player games, nothing can be saved locally on the player’s device because it can be modified, hacked, or lost.

This chapter introduces the fundamentals of persistence for game servers, including:

• Player data modeling
• Inventory & economy systems
• Saving and loading data
• Databases for games
• Event-driven persistence
• Preventing lost progress
• Scaling to millions of players

Persistence is one of the most important aspects of running an online game reliably and safely.