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11. Scaling MySQL > What Is Scalability?

What Is Scalability?

People often use terms such as “scalability,” “high availability,” and “performance” as synonyms in casual conversation, but they’re completely different. As we explained in Chapter 3, we define performance as response time. Scalability can be defined precisely too; we’ll explore that more fully in a moment, but in a nutshell it’s the system’s ability to deliver equal bang for the buck as you add resources to perform more work. Poorly scalable systems reach a point of diminishing returns and can’t grow further.

Capacity is a related concept. The system’s capacity is the amount of work it can perform in a given amount of time.[171] However, capacity must be qualified. The system’s maximum throughput is not the same as its capacity. Most benchmarks measure a system’s maximum throughput, but you can’t push real systems that hard. If you do, performance will degrade and response times will become unacceptably large and variable. We define the system’s actual capacity as the throughput it can achieve while still delivering acceptable performance. This is why benchmark results usually shouldn’t be reduced to a single number.


  

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