Design a gaming platform backend (leaderboard, matchmaking, inventory).

Leaderboard: Redis Sorted Set; ZADD game:season:1 score playerId; real-time top N Session: Redis Hash per session; game state for active matches Inventory: MongoDB for player item collections (flexible schema per item type) Matchmaking: Redis Sorted Set by skill rating; match nearby skill players Match history: Cassandra for immutable match records (high write, time-series) Player profile: MongoDB