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Metaspace Growth & ClassLoader GC Unloading

This experiment profiles native Metaspace allocation as hundreds of dynamic rule classes are compiled and verifies that Metaspace is fully reclaimed when RuleClassLoader instances are dereferenced.

Experiment Mechanics​

  1. Phase 1 (Allocation & Growth): Compiles $N$ unique rules, each defined in a dedicated RuleClassLoader. Monitors Metaspace growth from base (~33 MB) upward.
  2. Phase 2 (Dereferencing): Clears the cache and dereferences the ClassLoader instances.
  3. Phase 3 (GC Trigger & Verification): Invokes System.gc() and verifies that Metaspace usage drops back to initial baseline levels.

Experiment Output Example​

./scripts/start-helix.sh experiment --name metaspace --output json
{
  "experiment" : "METASPACE",
  "status" : "SUCCESS",
  "scenario" : "Metaspace Growth vs Classloader GC Unloading",
  "metaspaceReclaimedMB" : "12.4 MB"
}
Production Protection

Always configure -XX:MaxMetaspaceSize=256m in production to prevent unbounded native memory expansion if dynamic rules are loaded without proper cache bounds.