Scalability is the capacity of a system, process or business to handle increased load or growth while keeping performance and cost per unit under control.
Why it matters
A scalable product can serve ten times as many users without ten times the cost. On the technical side that means servers, databases and code that cope with traffic spikes; on the business side it means processes that do not rely on adding staff for every new customer. Scalability is often tested by simulating higher load and watching response times, error rates and costs, then fixing the slowest component first.
Example
A site works fine with 100 visitors but its pages take 8 seconds at 5,000 visitors because every request queries the database. Adding caching and a load balancer lets it serve 5,000 visitors with pages loading in under 2 seconds.
Common mistakes
- Optimizing for scale before there are users.
- Assuming scaling up (a bigger server) is enough when scaling out is needed.
- Ignoring manual business processes that will not scale.
Related
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This page is general information written by our editorial team and updated when documentation changes. Servers and providers differ, so test changes safely first. See our editorial policy and disclaimer.