{"abstract":"A read returns the newest physical version even though that version was not visible at the reader's snapshot.","category":"Storage and queries","checks":7,"contract":"Versions are [key,commit_sequence,value], with integer commit sequences unique within a key. Return a map from key to the value at its greatest sequence <= cutoff; omit keys with no visible version. Input storage order is arbitrary.","evaluation_group":"model-944670c98f51863b","failed_approach":"Filtering out future commits but taking the first surviving row depends on arbitrary storage order and can return an older value.","family":"store-snapshot-visible-version","id":"FA-126","implementations":{"attempt":{"sha256":"e2c747574cfcebf9a86ec5fa633a11ff92443973bad0607d5f01a05207d2fe92","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(versions, cutoff):\n    chosen = {}\n    for key, seq, value in versions:\n        if seq <= cutoff and key not in chosen:\n            chosen[key] = value\n    return chosen\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\nbase = 10*N\ncheck('future committed version is invisible', solve([['a', base, 'seen'], ['a', base+1, 'future']], base), {'a': 'seen'})\ncheck('old physical row does not win', solve([['a', base-1, 'old'], ['a', base, 'new']], base), {'a': 'new'})\ncheck('descending storage order is also valid', solve([['a', base+2, 'later'], ['a', base, N], ['a', base-2, 'old']], base), {'a': N})\ncheck('each key has its own newest visible version', solve([['a', base, 1], ['b', base-1, 2], ['a', base+1, 3]], base), {'a': 1, 'b': 2})\ncheck('key first created after cutoff is absent', solve([['a', base+1, N]], base), {})\ncheck('nullable value remains a visible row', solve([['a', base, None]], base), {'a': None})\ncheck('empty version history', solve([], base), {})\nprint(json.dumps({\"observations\": observations, \"passed\": all(x[\"passed\"] for x in observations)}, ensure_ascii=False))\nraise SystemExit(0 if all(x[\"passed\"] for x in observations) else 1)\n"},"broken":{"sha256":"7d22c530ffcd56b27510b69c142724458a3311c313374c58d547deacb761280f","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(versions, cutoff):\n    chosen = {}\n    for key, seq, value in versions:\n        if key not in chosen or seq > chosen[key][0]:\n            chosen[key] = (seq, value)\n    return {key: pair[1] for key, pair in chosen.items()}\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\nbase = 10*N\ncheck('future committed version is invisible', solve([['a', base, 'seen'], ['a', base+1, 'future']], base), {'a': 'seen'})\ncheck('old physical row does not win', solve([['a', base-1, 'old'], ['a', base, 'new']], base), {'a': 'new'})\ncheck('descending storage order is also valid', solve([['a', base+2, 'later'], ['a', base, N], ['a', base-2, 'old']], base), {'a': N})\ncheck('each key has its own newest visible version', solve([['a', base, 1], ['b', base-1, 2], ['a', base+1, 3]], base), {'a': 1, 'b': 2})\ncheck('key first created after cutoff is absent', solve([['a', base+1, N]], base), {})\ncheck('nullable value remains a visible row', solve([['a', base, None]], base), {'a': None})\ncheck('empty version history', solve([], base), {})\nprint(json.dumps({\"observations\": observations, \"passed\": all(x[\"passed\"] for x in observations)}, ensure_ascii=False))\nraise SystemExit(0 if all(x[\"passed\"] for x in observations) else 1)\n"},"fixed":{"sha256":"388a2c3be862b3e79ee6111decb0bfc52ca3753d7a0ef8bdcfaeaea7067555bd","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(versions, cutoff):\n    chosen = {}\n    for key, seq, value in versions:\n        if seq <= cutoff and (key not in chosen or seq > chosen[key][0]):\n            chosen[key] = (seq, value)\n    return {key: pair[1] for key, pair in chosen.items()}\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\nbase = 10*N\ncheck('future committed version is invisible', solve([['a', base, 'seen'], ['a', base+1, 'future']], base), {'a': 'seen'})\ncheck('old physical row does not win', solve([['a', base-1, 'old'], ['a', base, 'new']], base), {'a': 'new'})\ncheck('descending storage order is also valid', solve([['a', base+2, 'later'], ['a', base, N], ['a', base-2, 'old']], base), {'a': N})\ncheck('each key has its own newest visible version', solve([['a', base, 1], ['b', base-1, 2], ['a', base+1, 3]], base), {'a': 1, 'b': 2})\ncheck('key first created after cutoff is absent', solve([['a', base+1, N]], base), {})\ncheck('nullable value remains a visible row', solve([['a', base, None]], base), {'a': None})\ncheck('empty version history', solve([], base), {})\nprint(json.dumps({\"observations\": observations, \"passed\": all(x[\"passed\"] for x in observations)}, ensure_ascii=False))\nraise SystemExit(0 if all(x[\"passed\"] for x in observations) else 1)\n"}},"limitations":" 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.","method":"Deterministic executable model with adversarial boundary fixtures.","provenance":{"created_by":"Failure Map","dependencies":"Python standard library","family":"store-snapshot-visible-version","generated_at":"2026-09-29T14:36:50.502431+00:00","license":"CC0-1.0","python":"3.12.14","seed":1,"split":"open-access"},"relevance":"A deterministic committed-version visibility model for snapshot reads. It deliberately omits uncommitted transactions, transaction-ID wraparound, write conflict detection and real engine concurrency.","repair":"Filter versions by commit visibility, then select the greatest eligible commit sequence independently for every key.","root_cause":"Physical recency is used instead of the greatest commit sequence that is at or before the snapshot cutoff.","sha256":"d7e4e73dcb3d4daf06f4eda7f766283490344462d90e76e3dfb3874286810179","title":"A snapshot read selects a version committed after its cutoff · case 01","variant":1,"variant_policy":"Five numbered records share a model and may reuse boundary fixtures.","verification":{"attempt":{"elapsed_ms":35.11,"exit_code":1,"observations":[{"actual":{"a":"seen"},"check":"future committed version is invisible","expected":{"a":"seen"},"passed":true},{"actual":{"a":"old"},"check":"old physical row does not win","expected":{"a":"new"},"passed":false},{"actual":{"a":1},"check":"descending storage order is also valid","expected":{"a":1},"passed":true},{"actual":{"a":1,"b":2},"check":"each key has its own newest visible version","expected":{"a":1,"b":2},"passed":true},{"actual":{},"check":"key first created after cutoff is absent","expected":{},"passed":true},{"actual":{"a":null},"check":"nullable value remains a visible row","expected":{"a":null},"passed":true},{"actual":{},"check":"empty version history","expected":{},"passed":true}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"future committed version is invisible\", \"actual\": {\"a\": \"seen\"}, \"expected\": {\"a\": \"seen\"}, \"passed\": true}, {\"check\": \"old physical row does not win\", \"actual\": {\"a\": \"old\"}, \"expected\": {\"a\": \"new\"}, \"passed\": false}, {\"check\": \"descending storage order is also valid\", \"actual\": {\"a\": 1}, \"expected\": {\"a\": 1}, \"passed\": true}, {\"check\": \"each key has its own newest visible version\", \"actual\": {\"a\": 1, \"b\": 2}, \"expected\": {\"a\": 1, \"b\": 2}, \"passed\": true}, {\"check\": \"key first created after cutoff is absent\", \"actual\": {}, \"expected\": {}, \"passed\": true}, {\"check\": \"nullable value remains a visible row\", \"actual\": {\"a\": null}, \"expected\": {\"a\": null}, \"passed\": true}, {\"check\": \"empty version history\", \"actual\": {}, \"expected\": {}, \"passed\": true}], \"passed\": false}\n"},"broken":{"elapsed_ms":35.322,"exit_code":1,"observations":[{"actual":{"a":"future"},"check":"future committed version is invisible","expected":{"a":"seen"},"passed":false},{"actual":{"a":"new"},"check":"old physical row does not win","expected":{"a":"new"},"passed":true},{"actual":{"a":"later"},"check":"descending storage order is also valid","expected":{"a":1},"passed":false},{"actual":{"a":3,"b":2},"check":"each key has its own newest visible version","expected":{"a":1,"b":2},"passed":false},{"actual":{"a":1},"check":"key first created after cutoff is absent","expected":{},"passed":false},{"actual":{"a":null},"check":"nullable value remains a visible row","expected":{"a":null},"passed":true},{"actual":{},"check":"empty version history","expected":{},"passed":true}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"future committed version is invisible\", \"actual\": {\"a\": \"future\"}, \"expected\": {\"a\": \"seen\"}, \"passed\": false}, {\"check\": \"old physical row does not win\", \"actual\": {\"a\": \"new\"}, \"expected\": {\"a\": \"new\"}, \"passed\": true}, {\"check\": \"descending storage order is also valid\", \"actual\": {\"a\": \"later\"}, \"expected\": {\"a\": 1}, \"passed\": false}, {\"check\": \"each key has its own newest visible version\", \"actual\": {\"a\": 3, \"b\": 2}, \"expected\": {\"a\": 1, \"b\": 2}, \"passed\": false}, {\"check\": \"key first created after cutoff is absent\", \"actual\": {\"a\": 1}, \"expected\": {}, \"passed\": false}, {\"check\": \"nullable value remains a visible row\", \"actual\": {\"a\": null}, \"expected\": {\"a\": null}, \"passed\": true}, {\"check\": \"empty version history\", \"actual\": {}, \"expected\": {}, \"passed\": true}], \"passed\": false}\n"},"fixed":{"elapsed_ms":64.236,"exit_code":0,"observations":[{"actual":{"a":"seen"},"check":"future committed version is invisible","expected":{"a":"seen"},"passed":true},{"actual":{"a":"new"},"check":"old physical row does not win","expected":{"a":"new"},"passed":true},{"actual":{"a":1},"check":"descending storage order is also valid","expected":{"a":1},"passed":true},{"actual":{"a":1,"b":2},"check":"each key has its own newest visible version","expected":{"a":1,"b":2},"passed":true},{"actual":{},"check":"key first created after cutoff is absent","expected":{},"passed":true},{"actual":{"a":null},"check":"nullable value remains a visible row","expected":{"a":null},"passed":true},{"actual":{},"check":"empty version history","expected":{},"passed":true}],"passed":true,"stderr":"","stdout":"{\"observations\": [{\"check\": \"future committed version is invisible\", \"actual\": {\"a\": \"seen\"}, \"expected\": {\"a\": \"seen\"}, \"passed\": true}, {\"check\": \"old physical row does not win\", \"actual\": {\"a\": \"new\"}, \"expected\": {\"a\": \"new\"}, \"passed\": true}, {\"check\": \"descending storage order is also valid\", \"actual\": {\"a\": 1}, \"expected\": {\"a\": 1}, \"passed\": true}, {\"check\": \"each key has its own newest visible version\", \"actual\": {\"a\": 1, \"b\": 2}, \"expected\": {\"a\": 1, \"b\": 2}, \"passed\": true}, {\"check\": \"key first created after cutoff is absent\", \"actual\": {}, \"expected\": {}, \"passed\": true}, {\"check\": \"nullable value remains a visible row\", \"actual\": {\"a\": null}, \"expected\": {\"a\": null}, \"passed\": true}, {\"check\": \"empty version history\", \"actual\": {}, \"expected\": {}, \"passed\": true}], \"passed\": true}\n"}},"verified":true,"visibility":"public"}