Reading memory graphs

Production and local charts tell stories. Learn two shapes:

Healthy: sawtooth

Memory rises during work, drops after GC, returns near baseline.

xychart-beta
  title "Healthy sawtooth"
  x-axis [t1, t2, t3, t4, t5, t6, t7, t8]
  y-axis "Heap MB" 0 --> 50
  line [20, 35, 22, 38, 24, 36, 23, 37]

Leaking: staircase

Each cycle’s trough is higher than the last — GC cannot reclaim leaked objects.

xychart-beta
  title "Leak staircase"
  x-axis [t1, t2, t3, t4, t5, t6, t7, t8]
  y-axis "Heap MB" 0 --> 80
  line [20, 32, 38, 48, 55, 62, 70, 78]

How to validate

1. Steady synthetic load (same endpoint, same UI loop)
2. Mark deploy times on chart
3. Compare 7-day trend vs 24-hour noise
4. Correlate with traffic — leak persists at constant RPS

False positives

Pattern	Explanation
Step up after deploy	New code caches warmup — may be OK
Slow climb then flat	Cache reached steady state
Spike at cron time	Batch job — not necessarily leak

Alert on trend

Alert when heapUsed 7-day linear regression slope > threshold, not single spikes.