Requirements and game rules in LLD - Scalability & System Analysis

Scalability Analysis - Requirements and game rules

Growth Table: Users and System Changes

Scale	Users	Key Changes
Small	100 users	Basic game logic runs on a single server. Simple rules enforcement. Minimal latency. No complex scaling needed.
Medium	10,000 users	Multiple game sessions run concurrently. Need load balancing. Game state stored in memory or fast DB. Basic matchmaking introduced.
Large	1,000,000 users	Distributed game servers. Sharded game state storage. Advanced matchmaking and player ranking. Real-time synchronization challenges.
Very Large	100,000,000 users	Global data centers. CDN for static assets. Complex sharding and caching. Eventual consistency for some game states. High availability and fault tolerance.

First Bottleneck

At around 10,000 users, the first bottleneck is the game state management. The server's memory and CPU struggle to keep all active game sessions updated and consistent in real-time. This happens because game rules require frequent state changes and validations, which are CPU and memory intensive.

Scaling Solutions

• Horizontal scaling: Add more game servers to distribute player sessions and reduce load per server.
• State sharding: Partition game state by player groups or regions to reduce data size per server.
• Caching: Use in-memory caches for frequently accessed game rules and player data to speed up validation.
• Load balancing: Distribute incoming player connections evenly to avoid server overload.
• Asynchronous processing: Offload non-critical game rule checks to background jobs to reduce latency.

Back-of-Envelope Cost Analysis

• Requests per second: For 10,000 users playing actively, estimate ~50,000 game state updates per second (5 updates per user per second).
• Storage: Game state storage depends on game complexity; estimate 1 KB per player state -> 10 MB for 10,000 users in memory.
• Bandwidth: Each update ~500 bytes -> 25 MB/s outbound bandwidth needed at 10,000 users.

Interview Tip

When discussing scalability for game rules and requirements, start by clarifying the game's real-time needs and user concurrency. Identify the critical path where game state updates happen. Then, explain how you would scale the system step-by-step: from single server to distributed servers, state sharding, caching, and load balancing. Always justify your choices based on the bottleneck you identify.

Self Check

Your database handles 1000 queries per second (QPS). Game traffic grows 10x to 10,000 QPS. What do you do first?

Answer: Add read replicas and implement caching for frequently read game data to reduce load on the primary database. Also, consider sharding the database by player regions or game sessions to distribute write load.

Key Result

Game state management becomes the first bottleneck at medium scale (~10K users) due to CPU and memory load from frequent updates; scaling requires horizontal server scaling, state sharding, caching, and load balancing.

Practice

1. What is the main purpose of requirements in game design?

easy

A. To describe what the game must do

B. To explain how players should play

C. To decide the game's graphics style

D. To set the game's price

Solution

1. Step 1: Understand the role of requirements

   Requirements define the features and functions the game must have to work properly.

2. Step 2: Differentiate from rules

   Rules tell players how to play, not what the game must do technically.

3. Final Answer:

   To describe what the game must do -> Option A

4. Quick Check:

   Requirements = what game must do [OK]

Hint: Requirements = what game must do, rules = how to play [OK]

Common Mistakes:

• Confusing requirements with rules
• Thinking requirements set player behavior
• Mixing technical needs with gameplay instructions

2. Which of the following is a correct way to write a game rule?

easy

A. The game must load in under 5 seconds

B. Players must collect 10 coins to win

C. Use a database to store player scores

D. The game engine should support 3D graphics

Solution

1. Step 1: Identify what a game rule is

   A game rule tells players what they must or must not do during play.

2. Step 2: Check each option

   Players must collect 10 coins to win is a player instruction (rule). Options B, C, D are technical requirements.

3. Final Answer:

   Players must collect 10 coins to win -> Option B

4. Quick Check:

   Rules = player instructions [OK]

Hint: Rules tell players what to do, not technical details [OK]

Common Mistakes:

• Confusing technical requirements with rules
• Writing rules as system features
• Ignoring player actions in rules

3. Given these statements, which one is a requirement rather than a rule?
1. Players can jump over obstacles.
2. The game must save progress automatically.
3. Players lose a life if they touch spikes.
4. The game ends after 3 levels.

medium

A. The game must save progress automatically

B. Players lose a life if they touch spikes

C. Players can jump over obstacles

D. The game ends after 3 levels

Solution

1. Step 1: Identify requirements vs rules

   Requirements describe system features; rules describe player actions and consequences.

2. Step 2: Analyze each statement

   Statement 2 is a system feature (requirement). Others describe player actions (rules).

3. Final Answer:

   The game must save progress automatically -> Option A

4. Quick Check:

   Requirement = system feature [OK]

Hint: Requirements = system features; rules = player actions [OK]

Common Mistakes:

• Mixing player actions with system features
• Choosing rules as requirements
• Ignoring automatic system behaviors

4. A game designer wrote this rule: Players must collect 5 coins to win. But players can win without coins. What is the likely problem?

medium

A. The game has too many levels

B. The requirement is missing

C. The rule is not enforced in the game logic

D. The game has a syntax error

Solution

1. Step 1: Understand the problem

   The rule says players must collect coins, but they can win without doing so.

2. Step 2: Identify cause

   This means the game logic does not enforce the rule properly.

3. Final Answer:

   The rule is not enforced in the game logic -> Option C

4. Quick Check:

   Rule enforcement = game logic implementation [OK]

Hint: If rule ignored, check game logic enforcement [OK]

Common Mistakes:

• Confusing missing requirement with rule enforcement
• Assuming syntax error causes rule failure
• Ignoring game logic role

5. You want to design a fair multiplayer game. Which combination best ensures fairness and fun?

hard

A. Flexible rules with no system requirements

B. Complex rules that confuse players and minimal system requirements

C. No rules but strict technical requirements

D. Clear rules for player actions and balanced requirements for system performance

Solution

1. Step 1: Define fairness and fun

   Fairness needs clear rules; fun needs smooth system performance (requirements).

2. Step 2: Evaluate options

   Clear rules for player actions and balanced requirements for system performance combines clear player rules and balanced system needs, ensuring fairness and fun.

3. Final Answer:

   Clear rules for player actions and balanced requirements for system performance -> Option D

4. Quick Check:

   Fairness + fun = clear rules + balanced requirements [OK]

Hint: Fair game = clear rules + balanced system needs [OK]

Common Mistakes:

• Choosing complex or missing rules
• Ignoring system performance impact
• Separating rules from requirements