🏗️ Foundations · Days 1–6
Day 5: Reading the Numbers
Objective
Build a results summary (table + simple graph) and interpret what the numbers mean.
Scenario
Run a 10-minute test at moderate load. Study the results table: response times, throughput, error count, standard deviation. Sketch a simple graph or use built-in reporting.
Metrics to Watch
When It Clicks
Throughput and response time move in opposite directions as load grows.
Solution
Run 10 minutes at 10-20 users. In JMeter's Aggregate Report: note that p90 and p99 diverge from the mean as load grows - this is the 'long tail'. Standard deviation above 20% of the mean signals instability. Throughput (req/s) is your server's sustained capacity at that concurrency. The single metric to show a developer is p95: it represents the worst experience 1 in 20 real users encounters.
Reflection
Which metric would you show to a developer to explain that the system is struggling?
Deliverable
A one-page summary of your test results with annotations.
⚠️ Never run load tests against infrastructure you do not own or have explicit written permission to test. Always use a dedicated test environment. Unauthorized load injection can cause outages, trigger legal liability, and violate terms of service.