Performance vs scalability

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.^{<a href=http://www.allthingsdistributed.com/2006/03/a_word_on_scalability.html>1}

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.

Source(s) and further reading

• A word on scalability
• Scalability, availability, stability, patterns