Caching

// Definition

Storing the result of an expensive operation (a database query, an API call, a rendered page) so subsequent requests can be served faster without repeating the work. Caching introduces a class of test-specific bugs: stale data shown after an update, cache invalidation failures (old data persists after it should have been evicted), and CDN edge-cache inconsistencies where different users see different versions. Test strategy: verify freshness after writes, verify cache is bypassed when it should be (e.g. authenticated vs. public), and test behaviour when the cache layer is cold or unavailable.

// Related terms

• Latency

  The time between sending a request and receiving the first byte of response. Lower is better. Often reported at percentiles (p50, p95, p99) since averages hide tail behaviour.

• Response Time

  Total time from request initiation to response completion. Includes latency plus transfer and processing time. The end-user-perceived performance metric.

• Load Testing

  Verifying system behaviour under expected production load. Confirms the application meets performance targets at typical concurrent-user counts before release.