KimDoubleB Analyzing k6 Test Results
Interpret k6 test output, identify performance bottlenecks, and provide optimization recommendations.
Analysis Workflow
- Review summary output — Check overall pass/fail, iteration count, VU count
- Check thresholds — Which passed/failed? By how much?
- Analyze response times — Look at p50, p90, p95, p99 distribution
- Break down request duration — Examine blocked, connecting, TLS, waiting, receiving
- Identify bottlenecks — Map timing components to root causes
- Suggest optimizations — Script improvements, threshold tuning, infrastructure changes
Understanding k6 Output
End-of-Test Summary
data_received..................: 148 kB 4.9 kB/s
data_sent......................: 17 kB 564 B/s
http_req_blocked...............: avg=23.38ms min=1µs med=5µs max=235.44ms p(90)=10µs p(95)=210.47ms
http_req_connecting............: avg=11.12ms min=0s med=0s max=117.4ms p(90)=0s p(95)=99.38ms
✓ http_req_duration..............: avg=131.01ms min=116.4ms med=127.6ms max=196.38ms p(90)=146.21ms p(95)=176.91ms
http_req_failed................: 0.00% ✓ 0 ✗ 200
http_req_receiving.............: avg=5.11ms min=26µs med=4.88ms max=14.82ms p(90)=9.31ms p(95)=10.82ms
http_req_sending...............: avg=27µs min=4µs med=23µs max=240µs p(90)=42µs p(95)=66µs
http_req_tls_handshaking.......: avg=11.7ms min=0s med=0s max=116.76ms p(90)=0s p(95)=105.06ms
http_req_waiting...............: avg=125.86ms min=116.27ms med=122.6ms max=185.5ms p(90)=137.21ms p(95)=170.53ms
http_reqs......................: 200 6.63/s
iteration_duration.............: avg=1.16s min=1.12s med=1.13s max=1.43s p(90)=1.15s p(95)=1.41s
iterations.....................: 200 6.63/s
vus............................: 10 min=10 max=10
vus_max........................: 10 min=10 max=10
Reading the Output
- ✓ = threshold passed, ✗ = threshold failed
- Each metric shows:
avg,min,med(median),max,p(90),p(95) http_reqsrate = requests per second (RPS)
HTTP Request Duration Breakdown
The total http_req_duration is composed of:
blocked → connecting → tls_handshaking → sending → waiting → receiving
↑
(TTFB / server time)
| Component | What It Measures | Typical Cause of High Values |
|---|---|---|
http_req_blocked |
Time in queue before request starts | Connection pool exhaustion, DNS lookup |
http_req_connecting |
TCP connection time | Network latency, server far away |
http_req_tls_handshaking |
TLS/SSL handshake | Missing keep-alive, new connections per request |
http_req_sending |
Time to send request body | Large request body, slow upload |
http_req_waiting |
Server processing time (TTFB) | Slow backend, DB queries, server overload |
http_req_receiving |
Time to download response | Large response body, slow network |
http_req_duration |
sending + waiting + receiving | Overall request time |
See reference/bottleneck-patterns.md for detailed bottleneck analysis patterns.
Key Metrics Quick Reference
See reference/metrics.md for the complete k6 metrics reference.
Most Important Metrics to Monitor
| Metric | Type | What to Watch |
|---|---|---|
http_req_duration |
Trend | p95 and p99 — are they within SLA? |
http_req_failed |
Rate | Error rate — should be < 1% for normal load |
http_reqs |
Counter | Request rate (RPS) — is target throughput achieved? |
iteration_duration |
Trend | Full iteration time including sleeps |
checks |
Rate | Assertion pass rate — should be > 99% |
vus |
Gauge | Active VU count — did it reach target? |
Percentile Interpretation
| Percentile | Meaning |
|---|---|
p(50) / med |
Half of requests are faster. Typical user experience. |
p(90) |
90% of requests are faster. Most users' experience. |
p(95) |
95% of requests are faster. Common SLA target. |
p(99) |
99% of requests are faster. Worst-case for most users. |
p(99.9) |
1 in 1000 requests slower. Tail latency. |
Rule of thumb: If p95 is 2x+ the median, there's likely a bottleneck affecting some requests.
handleSummary() Customization
Override the default summary output:
import { textSummary } from 'https://jslib.k6.io/k6-summary/0.1.0/index.js';
export function handleSummary(data) {
return {
'summary.json': JSON.stringify(data, null, 2),
stdout: textSummary(data, { indent: ' ', enableColors: true }),
};
}
Available output targets:
stdout— Console outputstderr— Error output'filename.json'— Write to file'filename.html'— Write HTML report
Results Output Options
JSON Lines (Real-Time)
k6 run --out json=results.json script.js
CSV Output
k6 run --out csv=results.csv script.js
Web Dashboard (Built-in)
K6_WEB_DASHBOARD=true k6 run script.js
# Dashboard at http://localhost:5665
Grafana Cloud k6
k6 cloud run --local-execution script.js
# Or set K6_CLOUD_TOKEN environment variable
See reference/visualization.md for detailed visualization options.
Related Skills
- For designing test scenarios and thresholds:
/k6:designing-test-scenarios - For generating test scripts:
/k6:generating-api-load-tests