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Scalability
Scalability is how well a system keeps performing as load increases — more users, more data, more requests per second. Two common strategies:
- Vertical scaling — a bigger server (more CPU/RAM). Simple, but has a ceiling.
- Horizontal scaling — more servers running the same application behind a load balancer. More complex, but scales much further.
Caching (storing a slow computation's result temporarily) and database indexing are usually far higher-impact than either, and should typically be addressed first.