2 min lesson
Change-point detection over static thresholds
Use "Change-point detection over static thresholds" to tell the cases apart, then choose a response for each one.
Step 1 of 3
Change-point detection over static thresholds
A fixed threshold like "alert if p95 > 4s" breaks both ways. Change-point detection asks a better question: did the distribution's behavior shift at some point in time, relative to its own recent history?
Static threshold
"Alert if error rate > 1%."
Deaf to p95 moving from 800ms to 1.6s, or error rate tripling from 0.2% to 0.6%, when neither crosses the line.
Fires on every legitimate traffic shift and needs constant hand-tuning per metric and segment.
Change-point / anomaly
"Alert when the series departs its own recent baseline."
Catches relative shifts at any absolute level.
Adapts as baselines drift with traffic and seasonality.