FA-90652 / Garbage collector invariants / Member archive

Collection set: selection skips over regions that do not fit · case 02

Cheaper, less profitable regions are packed in after a better region was rejected.

Member previewVariant 2 · 3 implementations · 7 checks per implementation

Case contract

Regions are [id, kind, used, live]. All young regions are always collected (their live bytes cost live * cost). Old regions whose liveness is strictly below live_pct percent (live * 100 < pct * used) are candidates; humongous regions never are. Candidates are ordered by reclaimable bytes (used - live) descending, ties by id, and added while the accumulated cost stays within budget; selection stops at the first candidate that does not fit. Return the collection set, its cost and reclaimed bytes.

Why this case matters

Region-based collectors meet pause goals by choosing the collection set against a cost budget.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
expensive region first stops selection	`{"cset": [1, 2, 7, 3], "reclaimed": 335, "time": 65}`	`{"cset": [1, 2], "reclaimed": 160, "time": 40}`	Failed

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