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FA-45051 / Data systems / Open access

Batch fetch reads the beginning of a partially consumed batch · case 01

Batch fetch reads the beginning of a partially consumed batch.

Verified by executionVariant 1 · 8 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

batch-resume-cursor: Batch fetch reads the beginning of a partially consumed batch.

THE FAILURE

batch-resume-cursor: Batch fetch reads the beginning of a partially consumed batch.

Unsuccessful approach: Reading the last row also ignores the resume offset.

Case contract

Fetch at most quota rows from a sequence of batches starting at [batch-index,row-offset]. Skip exhausted and empty batches, return the emitted rows and a canonical next cursor, and mark exhaustion as [number-of-batches,0]. Quota zero preserves a normalized cursor.

Why this case matters

A bounded deterministic data engine model makes representation and changelog faults reproducible.

1 / The failure

Exit 1
"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(d):
    try:
        batches,batch,offset,quota=d
        out=[]
        while batch<len(batches) and offset>=len(batches[batch]):
            batch+=1; offset=0
        while quota>0 and batch<len(batches):
            out.append(batches[batch][0])
            offset+=1; quota-=1
            while batch<len(batches) and offset>=len(batches[batch]):
                batch+=1; offset=0
        return [out,[batch,offset]]
    except (IndexError, KeyError, ValueError, StopIteration) as exc:
        return {"representation_error": type(exc).__name__}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
if N == 1:
    check('partial current batch', solve([[[1, 2, 3]], 0, 1, 1]), [[2], [0, 2]])
    check('cross empty batches', solve([[[1], [], [], [2, 3]], 0, 0, 2]), [[1, 2], [3, 1]])
    check('initial exhausted', solve([[[], [], [1, 2]], 0, 0, 1]), [[1], [2, 1]])
    check('resume past long batch', solve([[[1, 2], [3, 4]], 0, 0, 3]), [[1, 2, 3], [1, 1]])
    check('all exhausted', solve([[[1]], 0, 1, 3]), [[], [1, 0]])
    check('zero quota', solve([[[1, 2]], 0, 1, 0]), [[], [0, 1]])
    check('within long batch', solve([[[1, 2, 3, 4]], 0, 0, 2]), [[1, 2], [0, 2]])
    check('empty stream', solve([[], 0, 0, 2]), [[], [0, 0]])
elif N == 2:
    check('partial current batch', solve([[[2, 3, 4]], 0, 1, 1]), [[3], [0, 2]])
    check('cross empty batches', solve([[[2], [], [], [3, 4]], 0, 0, 2]), [[2, 3], [3, 1]])
    check('initial exhausted', solve([[[], [], [2, 3]], 0, 0, 1]), [[2], [2, 1]])
    check('resume past long batch', solve([[[2, 3], [4, 5]], 0, 0, 3]), [[2, 3, 4], [1, 1]])
    check('all exhausted', solve([[[2]], 0, 1, 3]), [[], [1, 0]])
    check('zero quota', solve([[[2, 3]], 0, 1, 0]), [[], [0, 1]])
    check('within long batch', solve([[[2, 3, 4, 5]], 0, 0, 2]), [[2, 3], [0, 2]])
    check('empty stream', solve([[], 0, 0, 2]), [[], [0, 0]])
elif N == 3:
    check('partial current batch', solve([[[3, 4, 5]], 0, 1, 1]), [[4], [0, 2]])
    check('cross empty batches', solve([[[3], [], [], [4, 5]], 0, 0, 2]), [[3, 4], [3, 1]])
    check('initial exhausted', solve([[[], [], [3, 4]], 0, 0, 1]), [[3], [2, 1]])
    check('resume past long batch', solve([[[3, 4], [5, 6]], 0, 0, 3]), [[3, 4, 5], [1, 1]])
    check('all exhausted', solve([[[3]], 0, 1, 3]), [[], [1, 0]])
    check('zero quota', solve([[[3, 4]], 0, 1, 0]), [[], [0, 1]])
    check('within long batch', solve([[[3, 4, 5, 6]], 0, 0, 2]), [[3, 4], [0, 2]])
    check('empty stream', solve([[], 0, 0, 2]), [[], [0, 0]])
elif N == 4:
    check('partial current batch', solve([[[4, 5, 6]], 0, 1, 1]), [[5], [0, 2]])
    check('cross empty batches', solve([[[4], [], [], [5, 6]], 0, 0, 2]), [[4, 5], [3, 1]])
    check('initial exhausted', solve([[[], [], [4, 5]], 0, 0, 1]), [[4], [2, 1]])
    check('resume past long batch', solve([[[4, 5], [6, 7]], 0, 0, 3]), [[4, 5, 6], [1, 1]])
    check('all exhausted', solve([[[4]], 0, 1, 3]), [[], [1, 0]])
    check('zero quota', solve([[[4, 5]], 0, 1, 0]), [[], [0, 1]])
    check('within long batch', solve([[[4, 5, 6, 7]], 0, 0, 2]), [[4, 5], [0, 2]])
    check('empty stream', solve([[], 0, 0, 2]), [[], [0, 0]])
elif N == 5:
    check('partial current batch', solve([[[5, 6, 7]], 0, 1, 1]), [[6], [0, 2]])
    check('cross empty batches', solve([[[5], [], [], [6, 7]], 0, 0, 2]), [[5, 6], [3, 1]])
    check('initial exhausted', solve([[[], [], [5, 6]], 0, 0, 1]), [[5], [2, 1]])
    check('resume past long batch', solve([[[5, 6], [7, 8]], 0, 0, 3]), [[5, 6, 7], [1, 1]])
    check('all exhausted', solve([[[5]], 0, 1, 3]), [[], [1, 0]])
    check('zero quota', solve([[[5, 6]], 0, 1, 0]), [[], [0, 1]])
    check('within long batch', solve([[[5, 6, 7, 8]], 0, 0, 2]), [[5, 6], [0, 2]])
    check('empty stream', solve([[], 0, 0, 2]), [[], [0, 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 fixtureActualExpectedOutcome
partial current batch[[1], [0, 2]][[2], [0, 2]]Failed
cross empty batches[[1, 2], [3, 1]][[1, 2], [3, 1]]Passed
initial exhausted[[1], [2, 1]][[1], [2, 1]]Passed
resume past long batch[[1, 1, 3], [1, 1]][[1, 2, 3], [1, 1]]Failed
all exhausted[[], [1, 0]][[], [1, 0]]Passed
zero quota[[], [0, 1]][[], [0, 1]]Passed
within long batch[[1, 1], [0, 2]][[1, 2], [0, 2]]Failed
empty stream[[], [0, 0]][[], [0, 0]]Passed

SHA-256 / 7f251611845d064c343eb7cf7e6e785ecd002b24e02aa7e770caaf482c01c915

2 / The unsuccessful fix

Exit 1
"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(d):
    try:
        batches,batch,offset,quota=d
        out=[]
        while batch<len(batches) and offset>=len(batches[batch]):
            batch+=1; offset=0
        while quota>0 and batch<len(batches):
            out.append(batches[batch][-1])
            offset+=1; quota-=1
            while batch<len(batches) and offset>=len(batches[batch]):
                batch+=1; offset=0
        return [out,[batch,offset]]
    except (IndexError, KeyError, ValueError, StopIteration) as exc:
        return {"representation_error": type(exc).__name__}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
if N == 1:
    check('partial current batch', solve([[[1, 2, 3]], 0, 1, 1]), [[2], [0, 2]])
    check('cross empty batches', solve([[[1], [], [], [2, 3]], 0, 0, 2]), [[1, 2], [3, 1]])
    check('initial exhausted', solve([[[], [], [1, 2]], 0, 0, 1]), [[1], [2, 1]])
    check('resume past long batch', solve([[[1, 2], [3, 4]], 0, 0, 3]), [[1, 2, 3], [1, 1]])
    check('all exhausted', solve([[[1]], 0, 1, 3]), [[], [1, 0]])
    check('zero quota', solve([[[1, 2]], 0, 1, 0]), [[], [0, 1]])
    check('within long batch', solve([[[1, 2, 3, 4]], 0, 0, 2]), [[1, 2], [0, 2]])
    check('empty stream', solve([[], 0, 0, 2]), [[], [0, 0]])
elif N == 2:
    check('partial current batch', solve([[[2, 3, 4]], 0, 1, 1]), [[3], [0, 2]])
    check('cross empty batches', solve([[[2], [], [], [3, 4]], 0, 0, 2]), [[2, 3], [3, 1]])
    check('initial exhausted', solve([[[], [], [2, 3]], 0, 0, 1]), [[2], [2, 1]])
    check('resume past long batch', solve([[[2, 3], [4, 5]], 0, 0, 3]), [[2, 3, 4], [1, 1]])
    check('all exhausted', solve([[[2]], 0, 1, 3]), [[], [1, 0]])
    check('zero quota', solve([[[2, 3]], 0, 1, 0]), [[], [0, 1]])
    check('within long batch', solve([[[2, 3, 4, 5]], 0, 0, 2]), [[2, 3], [0, 2]])
    check('empty stream', solve([[], 0, 0, 2]), [[], [0, 0]])
elif N == 3:
    check('partial current batch', solve([[[3, 4, 5]], 0, 1, 1]), [[4], [0, 2]])
    check('cross empty batches', solve([[[3], [], [], [4, 5]], 0, 0, 2]), [[3, 4], [3, 1]])
    check('initial exhausted', solve([[[], [], [3, 4]], 0, 0, 1]), [[3], [2, 1]])
    check('resume past long batch', solve([[[3, 4], [5, 6]], 0, 0, 3]), [[3, 4, 5], [1, 1]])
    check('all exhausted', solve([[[3]], 0, 1, 3]), [[], [1, 0]])
    check('zero quota', solve([[[3, 4]], 0, 1, 0]), [[], [0, 1]])
    check('within long batch', solve([[[3, 4, 5, 6]], 0, 0, 2]), [[3, 4], [0, 2]])
    check('empty stream', solve([[], 0, 0, 2]), [[], [0, 0]])
elif N == 4:
    check('partial current batch', solve([[[4, 5, 6]], 0, 1, 1]), [[5], [0, 2]])
    check('cross empty batches', solve([[[4], [], [], [5, 6]], 0, 0, 2]), [[4, 5], [3, 1]])
    check('initial exhausted', solve([[[], [], [4, 5]], 0, 0, 1]), [[4], [2, 1]])
    check('resume past long batch', solve([[[4, 5], [6, 7]], 0, 0, 3]), [[4, 5, 6], [1, 1]])
    check('all exhausted', solve([[[4]], 0, 1, 3]), [[], [1, 0]])
    check('zero quota', solve([[[4, 5]], 0, 1, 0]), [[], [0, 1]])
    check('within long batch', solve([[[4, 5, 6, 7]], 0, 0, 2]), [[4, 5], [0, 2]])
    check('empty stream', solve([[], 0, 0, 2]), [[], [0, 0]])
elif N == 5:
    check('partial current batch', solve([[[5, 6, 7]], 0, 1, 1]), [[6], [0, 2]])
    check('cross empty batches', solve([[[5], [], [], [6, 7]], 0, 0, 2]), [[5, 6], [3, 1]])
    check('initial exhausted', solve([[[], [], [5, 6]], 0, 0, 1]), [[5], [2, 1]])
    check('resume past long batch', solve([[[5, 6], [7, 8]], 0, 0, 3]), [[5, 6, 7], [1, 1]])
    check('all exhausted', solve([[[5]], 0, 1, 3]), [[], [1, 0]])
    check('zero quota', solve([[[5, 6]], 0, 1, 0]), [[], [0, 1]])
    check('within long batch', solve([[[5, 6, 7, 8]], 0, 0, 2]), [[5, 6], [0, 2]])
    check('empty stream', solve([[], 0, 0, 2]), [[], [0, 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 fixtureActualExpectedOutcome
partial current batch[[3], [0, 2]][[2], [0, 2]]Failed
cross empty batches[[1, 3], [3, 1]][[1, 2], [3, 1]]Failed
initial exhausted[[2], [2, 1]][[1], [2, 1]]Failed
resume past long batch[[2, 2, 4], [1, 1]][[1, 2, 3], [1, 1]]Failed
all exhausted[[], [1, 0]][[], [1, 0]]Passed
zero quota[[], [0, 1]][[], [0, 1]]Passed
within long batch[[4, 4], [0, 2]][[1, 2], [0, 2]]Failed
empty stream[[], [0, 0]][[], [0, 0]]Passed

SHA-256 / 2c47305ad9ce6a839de335fa836c9fb0b8bd848fb6f05a6eccaae55b2d92d777

HELD IN THE MEMBER ARCHIVE

The verified repair and its recorded checks are member-only.

This mechanism has 8 recorded checks per implementation. The open-access tier publishes the failure and the unsuccessful fix; the repaired source that passes every check, and the observations that prove it, are available to members.

Every case sharing this mechanism uses the same contract and the same repair, so this one record is held back for all of them.

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Verification & scope

Offline stipulated semantics over valid small inputs; no performance, concurrency, or production-engine conformance claim. 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 2026-09-29T14:44:18.307400+00:00.

Case digest / 3de030ecb30b804572644a2309661efe092da3ded091d61dee0ace83f7e6243f