Prometheus

PromQL Gotchas

Counter Functions (Critical)

Counters only increase. Never use raw counter values—always use rate functions:

rate(http_requests_total[5m])      # Per-second average rate
irate(http_requests_total[5m])     # Instant rate (last 2 points, spiky)
increase(http_requests_total[1h])  # Total increase over range

• rate() handles counter resets automatically
• Use rate() for dashboards, irate() only for high-resolution spikes

Range Vector Required

Rate functions need [duration]:

rate(metric[5m])    # Correct
rate(metric)        # Error: expected range vector