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Garbage Collection Reference Mechanics

This experiment evaluates the lifecycle differences between SoftReference (used in L2 Cache) and WeakReference (used in L3 Cache) under active memory pressure.

Behavior Comparison​

Soft Reference Formula​

HotSpot uses the -XX:SoftRefLRUPolicyMSPerMB JVM flag (default 1000) to determine when soft references expire:

Time to Clear (ms) = Free Heap Space (MB) * SoftRefLRUPolicyMSPerMB

For example, with 4,096 MB (4 GB) of free heap memory and default policy (1000 ms/MB), soft references survive for ~4,096 seconds (~68 minutes) before being candidates for eviction.

Experiment Output Example​

./scripts/run-experiment.sh gc
[INFO] Running GC Stress Experiment...
WeakReference Scenario: Initial = 10, Cleared = 10, Retained = 0
SoftReference Scenario: Initial = 10, Cleared = 0, Retained = 10 (Sufficient Heap Available)