FA-10396 / Caching / Open access

Weighted eviction frees fewer bytes than the new budget requires · case 01

Weighted eviction frees fewer bytes than the new budget requires.

Verified by executionVariant 1 · 4 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

One eviction is assumed to free enough space regardless of entry weight.

VERIFIED REPAIR

Preserve the cache-state invariant: Entries are [key,nonnegative weight] in eviction order. Remove a prefix until remaining weight is at most the nonnegative budget; retain zero-weight entries if no eviction is necessary.

Unsuccessful approach: An entry-count limit is substituted for a byte-weight budget.

Case contract

Entries are [key,nonnegative weight] in eviction order. Remove a prefix until remaining weight is at most the nonnegative budget; retain zero-weight entries if no eviction is necessary.

Why this case matters

A deterministic cache state transformation. Inputs are copied or treated as immutable; no remote storage, real clock, or concurrent interleaving is simulated.

1 / The failure

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(entries, budget):
    out=list(entries)
    if sum(w for k,w in out)>budget:
        out=out[1:]
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('fixture 1', solve(*([['a', 4], ['b', 3], ['c', 2]], 2)), [['c', 2]])
check('fixture 2', solve(*([['a', 4], ['b', 3]], 4)), [['b', 3]])
check('fixture 3', solve(*([], 0)), [])
check('fixture 4', solve(*([['a', 0], ['b', 0]], 0)), [['a', 0], ['b', 0]])
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)

Boundary fixture	Actual	Expected	Outcome
fixture 1	`[['b', 3], ['c', 2]]`	`[['c', 2]]`	Failed
fixture 2	`[['b', 3]]`	`[['b', 3]]`	Passed
fixture 3	`[]`	`[]`	Passed
fixture 4	`[['a', 0], ['b', 0]]`	`[['a', 0], ['b', 0]]`	Passed

SHA-256 / db9f34fc78caf221e6e414dc65637d7859c4842857cba52a6ffbc43de2a5419a

2 / The unsuccessful fix

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(entries, budget):
    out=list(entries)
    while len(out)>budget:
        out.pop(0)
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('fixture 1', solve(*([['a', 4], ['b', 3], ['c', 2]], 2)), [['c', 2]])
check('fixture 2', solve(*([['a', 4], ['b', 3]], 4)), [['b', 3]])
check('fixture 3', solve(*([], 0)), [])
check('fixture 4', solve(*([['a', 0], ['b', 0]], 0)), [['a', 0], ['b', 0]])
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)

Boundary fixture	Actual	Expected	Outcome
fixture 1	`[['b', 3], ['c', 2]]`	`[['c', 2]]`	Failed
fixture 2	`[['a', 4], ['b', 3]]`	`[['b', 3]]`	Failed
fixture 3	`[]`	`[]`	Passed
fixture 4	`[]`	`[['a', 0], ['b', 0]]`	Failed

SHA-256 / b101e10dd1c681942fa7a2a59558d4a9ce13ebca06aa7cdd347ae27a2077aeba

3 / The verified repair

Exit 0

"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(entries, budget):
    out=list(entries)
    while sum(w for k,w in out)>budget:
        out.pop(0)
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('fixture 1', solve(*([['a', 4], ['b', 3], ['c', 2]], 2)), [['c', 2]])
check('fixture 2', solve(*([['a', 4], ['b', 3]], 4)), [['b', 3]])
check('fixture 3', solve(*([], 0)), [])
check('fixture 4', solve(*([['a', 0], ['b', 0]], 0)), [['a', 0], ['b', 0]])
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)

Boundary fixture	Actual	Expected	Outcome
fixture 1	`[['c', 2]]`	`[['c', 2]]`	Passed
fixture 2	`[['b', 3]]`	`[['b', 3]]`	Passed
fixture 3	`[]`	`[]`	Passed
fixture 4	`[['a', 0], ['b', 0]]`	`[['a', 0], ['b', 0]]`	Passed

SHA-256 / ac58d53fbdec1687a2abb52b19f9cd0ac368c36162affed99005ba21f673d302

Verification & scope

This reproducer isolates one failure mechanism. Results cover the supplied fixtures. Variants within a family share a test contract and should remain grouped when constructing evaluation splits. Related mechanisms with a shared evaluation_group must also remain together; these controlled models are not independent production incidents.

Observations recorded using Python 3.12.14 at 2026-09-29T14:38:38.632379+00:00.

Case digest / f398403a68deee6edf6ecec3c8ac3ccaf905dc397d7ddd2beb50f44616c11059