Game Databases

Implement efficient data persistence for players, matches, and leaderboards.

Database Selection

Database	Strength	Use Case
PostgreSQL	ACID, complex queries	Player data, transactions
Redis	Ultra-fast	Leaderboards, cache, sessions
MongoDB	Flexible schema	Game logs, analytics
DynamoDB	Infinite scale	Global leaderboards
CockroachDB	Distributed ACID	Multi-region

PostgreSQL Schema

-- Player profiles
CREATE TABLE players (
    id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
    username VARCHAR(32) UNIQUE NOT NULL,
    email VARCHAR(255) UNIQUE NOT NULL,
    mmr INTEGER DEFAULT 1000,
    level INTEGER DEFAULT 1,
    xp INTEGER DEFAULT 0,
    coins BIGINT DEFAULT 0,
    created_at TIMESTAMP DEFAULT NOW(),
    last_login TIMESTAMP DEFAULT NOW()
);

-- Indexes for common queries
CREATE INDEX idx_players_mmr ON players(mmr DESC);
CREATE INDEX idx_players_level ON players(level DESC);

-- Inventory system
CREATE TABLE inventory (
    id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
    player_id UUID REFERENCES players(id) ON DELETE CASCADE,
    item_type VARCHAR(50) NOT NULL,
    item_id VARCHAR(100) NOT NULL,
    quantity INTEGER DEFAULT 1,
    metadata JSONB DEFAULT '{}',
    acquired_at TIMESTAMP DEFAULT NOW(),
    UNIQUE(player_id, item_type, item_id)
);

-- Match history
CREATE TABLE matches (
    id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
    game_mode VARCHAR(32) NOT NULL,
    started_at TIMESTAMP NOT NULL,
    ended_at TIMESTAMP,
    winner_team INTEGER,
    metadata JSONB DEFAULT '{}'
);

CREATE TABLE match_players (
    match_id UUID REFERENCES matches(id),
    player_id UUID REFERENCES players(id),
    team INTEGER NOT NULL,
    score INTEGER DEFAULT 0,
    kills INTEGER DEFAULT 0,
    deaths INTEGER DEFAULT 0,
    mmr_change INTEGER DEFAULT 0,
    PRIMARY KEY (match_id, player_id)
);

Redis Leaderboard

const Redis = require('ioredis');
const redis = new Redis({ host: 'localhost', port: 6379 });

class Leaderboard {
    constructor(name) {
        this.key = `leaderboard:${name}`;
    }

    async setScore(playerId, score) {
        return redis.zadd(this.key, score, playerId);
    }

    async getScore(playerId) {
        return redis.zscore(this.key, playerId);
    }

    async getRank(playerId) {
        // 0-indexed, null if not found
        const rank = await redis.zrevrank(this.key, playerId);
        return rank !== null ? rank + 1 : null;
    }

    async getTop(count = 100) {
        const results = await redis.zrevrange(
            this.key, 0, count - 1, 'WITHSCORES'
        );

        // Convert to [{playerId, score, rank}]
        const leaderboard = [];
        for (let i = 0; i < results.length; i += 2) {
            leaderboard.push({
                playerId: results[i],
                score: parseInt(results[i + 1]),
                rank: i / 2 + 1
            });
        }
        return leaderboard;
    }

    async getAroundPlayer(playerId, range = 5) {
        const rank = await this.getRank(playerId);
        if (!rank) return [];

        const start = Math.max(0, rank - range - 1);
        const end = rank + range - 1;

        return redis.zrevrange(this.key, start, end, 'WITHSCORES');
    }
}

Connection Pooling

const { Pool } = require('pg');

const pool = new Pool({
    host: process.env.DB_HOST,
    database: 'game',
    max: 20,                    // Max connections
    idleTimeoutMillis: 30000,   // Close idle connections
    connectionTimeoutMillis: 2000
});

// Transaction wrapper
async function withTransaction(callback) {
    const client = await pool.connect();
    try {
        await client.query('BEGIN');
        const result = await callback(client);
        await client.query('COMMIT');
        return result;
    } catch (e) {
        await client.query('ROLLBACK');
        throw e;
    } finally {
        client.release();
    }
}

// Usage: Atomic currency transfer
await withTransaction(async (client) => {
    await client.query(
        'UPDATE players SET coins = coins - $1 WHERE id = $2',
        [amount, senderId]
    );
    await client.query(
        'UPDATE players SET coins = coins + $1 WHERE id = $2',
        [amount, receiverId]
    );
});

Caching Strategy

class CachedPlayerService {
    constructor(db, redis) {
        this.db = db;
        this.redis = redis;
        this.ttl = 3600; // 1 hour
    }

    async getPlayer(playerId) {
        const cacheKey = `player:${playerId}`;

        // Try cache first
        const cached = await this.redis.get(cacheKey);
        if (cached) {
            return JSON.parse(cached);
        }

        // Cache miss - load from DB
        const player = await this.db.query(
            'SELECT * FROM players WHERE id = $1',
            [playerId]
        );

        if (player.rows[0]) {
            // Cache for future requests
            await this.redis.setex(
                cacheKey,
                this.ttl,
                JSON.stringify(player.rows[0])
            );
        }

        return player.rows[0];
    }

    async updatePlayer(playerId, updates) {
        // Update DB
        await this.db.query(
            'UPDATE players SET mmr = $1 WHERE id = $2',
            [updates.mmr, playerId]
        );

        // Invalidate cache
        await this.redis.del(`player:${playerId}`);
    }
}

Troubleshooting

Common Failure Modes

Error	Root Cause	Solution
Connection timeout	Pool exhausted	Increase pool size
Deadlock	Lock contention	Fix lock ordering
Slow queries	Missing index	Add indexes
Cache stampede	Mass expiration	Staggered TTL
Stale data	Cache inconsistency	Invalidation strategy

Debug Checklist

-- Check active connections
SELECT count(*) FROM pg_stat_activity WHERE datname = 'game';

-- Find slow queries
SELECT query, mean_time, calls
FROM pg_stat_statements
ORDER BY mean_time DESC LIMIT 10;

-- Check index usage
SELECT relname, seq_scan, idx_scan
FROM pg_stat_user_tables
WHERE seq_scan > idx_scan;

-- Table sizes
SELECT relname, pg_size_pretty(pg_total_relation_size(relid))
FROM pg_stat_user_tables ORDER BY pg_total_relation_size(relid) DESC;

# Redis diagnostics
redis-cli INFO stats
redis-cli SLOWLOG GET 10
redis-cli MEMORY DOCTOR

Unit Test Template

const { Pool } = require('pg');

describe('Database Operations', () => {
    let pool;

    beforeAll(async () => {
        pool = new Pool({ database: 'game_test' });
    });

    afterAll(async () => {
        await pool.end();
    });

    test('creates player with default values', async () => {
        const result = await pool.query(
            `INSERT INTO players (username, email)
             VALUES ($1, $2) RETURNING *`,
            ['testuser', 'test@example.com']
        );

        expect(result.rows[0].mmr).toBe(1000);
        expect(result.rows[0].level).toBe(1);
    });

    test('leaderboard returns correct rank', async () => {
        const lb = new Leaderboard('test');

        await lb.setScore('player1', 1000);
        await lb.setScore('player2', 2000);
        await lb.setScore('player3', 1500);

        expect(await lb.getRank('player2')).toBe(1);
        expect(await lb.getRank('player3')).toBe(2);
        expect(await lb.getRank('player1')).toBe(3);
    });

    test('transaction rollback on error', async () => {
        const initialCoins = 1000;

        try {
            await withTransaction(async (client) => {
                await client.query(
                    'UPDATE players SET coins = coins - 500 WHERE id = $1',
                    [playerId]
                );
                throw new Error('Simulated failure');
            });
        } catch (e) {
            // Expected
        }

        // Verify rollback
        const result = await pool.query(
            'SELECT coins FROM players WHERE id = $1',
            [playerId]
        );
        expect(result.rows[0].coins).toBe(initialCoins);
    });
});

Resources

• assets/ - Schema templates
• references/ - Database optimization guides