> ## Documentation Index
> Fetch the complete documentation index at: https://mintlify.com/donnemartin/system-design-primer/llms.txt
> Use this file to discover all available pages before exploring further.

# Performance vs scalability

> Understanding the difference between performance and scalability problems in distributed systems

A service is **scalable** if it results in increased **performance** in a manner proportional to resources added. Generally, increasing performance means serving more units of work, but it can also be to handle larger units of work, such as when datasets grow.

## Understanding the difference

Another way to look at performance vs scalability:

* If you have a **performance** problem, your system is slow for a single user.
* If you have a **scalability** problem, your system is fast for a single user but slow under heavy load.

<Note>
  A system that performs well for a single user but degrades under load has a scalability problem, not a performance problem.
</Note>

## Key concepts

### Performance

Performance refers to how quickly your system responds to requests. A performance problem means that even with minimal load (e.g., a single user), the system is slow.

Performance issues are typically addressed by:

* Optimizing algorithms
* Reducing computational complexity
* Improving database queries
* Minimizing network latency

### Scalability

Scalability refers to your system's ability to handle increased load by adding resources. A scalability problem means the system works well under light load but struggles as load increases.

Scalability issues are typically addressed by:

* Horizontal scaling (adding more servers)
* Load balancing
* Caching strategies
* Database sharding
* Asynchronous processing

## Why it matters

Understanding whether you have a performance or scalability problem is critical because the solutions are different:

* **Performance problems** require optimization of existing code and infrastructure
* **Scalability problems** require architectural changes to distribute load

<Info>
  It's possible to have both performance and scalability problems simultaneously. Address performance issues first, as they may be masking scalability problems.
</Info>

## Additional resources

* [A word on scalability](http://www.allthingsdistributed.com/2006/03/a_word_on_scalability.html)
* [Scalability, availability, stability, patterns](http://www.slideshare.net/jboner/scalability-availability-stability-patterns/)