When to use which creational pattern in LLD - Scalability & System Analysis

Scalability Analysis - When to use which creational pattern

Growth Table: Usage of Creational Patterns at Different Scales

Scale	Object Creation Needs	Pattern Usage	Impact on System
100 users	Few objects, simple creation	Simple Factory or direct instantiation	Minimal overhead, easy to maintain
10K users	More objects, need for flexibility	Factory Method or Builder for complex objects	Improved code reuse, easier object management
1M users	High object creation, performance critical	Singleton for shared resources, Prototype for cloning	Reduces resource usage, faster object creation
100M users	Massive scale, distributed systems	Abstract Factory with dependency injection, Singleton with distributed locks	Ensures consistency, scalable object management

First Bottleneck

At small scale, object creation overhead is negligible. As users grow, the bottleneck becomes inefficient object creation causing CPU and memory strain. For example, creating many complex objects repeatedly slows down the system. Without proper patterns, code becomes hard to maintain and extend.

Scaling Solutions

• Simple Factory: Use for small scale to centralize object creation.
• Factory Method: Use when subclasses decide object types, improving flexibility.
• Builder: Use for complex objects with many parts, improving readability and maintainability.
• Singleton: Use for shared resources to avoid multiple instances and save memory.
• Prototype: Use to clone objects efficiently instead of creating from scratch.
• Abstract Factory: Use in large systems to create families of related objects, supporting scalability and consistency.
• Combine with Dependency Injection: To manage object lifecycles and dependencies cleanly at scale.

Back-of-Envelope Cost Analysis

• At 10K users, creating 10 objects per user per second = 100K objects/sec.
• Without patterns, each creation costs CPU cycles and memory allocation.
• Using Prototype can reduce creation time by cloning, saving CPU.
• Singleton reduces memory by sharing instances.
• At 1M users, object creation can reach millions per second, stressing CPU and memory.
• Proper patterns reduce overhead and improve throughput.

Interview Tip

Start by explaining the problem of object creation at scale. Describe each creational pattern briefly and when it fits best. Use examples like shared resources (Singleton), complex object building (Builder), or flexible object families (Abstract Factory). Discuss bottlenecks and how patterns solve them. Show understanding of trade-offs and scalability.

Self Check

Your system creates 1000 objects per second. Traffic grows 10x to 10,000 objects per second. What do you do first?

Answer: Identify if object creation is a bottleneck. If yes, apply Prototype to clone objects or Singleton to share instances where possible. Consider Builder for complex objects to optimize creation steps. This reduces CPU and memory usage, improving scalability.

Key Result

Creational patterns help manage object creation efficiently as system scales, preventing CPU and memory bottlenecks by reusing, cloning, or centralizing object creation.