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Concept: Scalability

1. The Snapshot​

A system's ability to handle increased load (data, traffic, or complexity) by adding resources in a predictable way.

2. The Description​

Scalability is not a one-dimensional label ("X is scalable"). It is a description of how a system copes with growth. It requires defining load parameters (what is growing?) and performance metrics (what is the impact?) to determine the strategy for adding resources.

3. Author Quotes​

"scalability means considering questions like 'If the system grows in a particular way, what are our options for coping with the growth?' and 'How can we add computing resources to handle the additional load?'" (p. 11)

4. Defining Features​

  • Load Parameters: Describing current load (e.g., requests per second, ratio of reads/writes).
  • Performance Metrics: Observing what happens when load increases (e.g., response time percentiles).
  • Growth Strategy: Having a clear path to add resources (scaling up or out) to maintain performance.

5. The Boundary​

  • It is NOT a Binary State: A system isn't "scalable" or "not scalable." It's a question of how it scales under specific types of growth.
  • It is NOT just Performance: Performance is "fast for a given load." Scalability is "maintaining performance as load increases."

6. The Prototype​

Twitter's 2012 architecture change. The "fan-out" (write) load for celebrities became so high that the system couldn't scale by just adding more databases. They had to change the architecture to a "pull" model for those specific users.

7. Helpful Info​

A common mistake is designing for scalability prematurely. "Hypothetical scalability" often leads to complex, hard-to-maintain systems that are slower at low loads.

8. The Swap Test​

"To maintain Reliability as our user base grows, we must invest in Scalability to ensure our latency stays within acceptable bounds."

9. Source Reference​

ddia/pages/page_033.txt

🧠 Pedagogical Tracking​

MilestoneStatusDateLesson RefNotes
Introduced in Lesson⚪
Active Recall #1⚪
1-Day Review⚪
1-Week Review⚪
1-Month Review⚪