FA-711 / Replication / Open access

Acknowledge a replicated write concern: Multiple copies in one failure domain satisfy zone concern · case 01

The write concern operation is admitted even though multiple copies in one failure domain satisfy zone concern.

Verified by executionVariant 1 · 9 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

The admission path omits the failure domains invariant while validating the other operation preconditions.

THE FAILURE

The admission path omits the failure domains invariant while validating the other operation preconditions.

Unsuccessful approach: Adding the failure domains check repairs the reported defect, but replacing the adjacent write binding check loses that independent invariant.

Case contract

Return a Boolean admission decision for acknowledge a replicated write concern. The record r must satisfy all of: len(set(r['distinct_replicas'][0])) >= r['distinct_replicas'][1]; sum(r['durable_acks'][0]) >= r['durable_acks'][1]; len(set(r['failure_domains'][0])) >= r['failure_domains'][1]; all(x == r['write_binding'][0] for x in r['write_binding'][1]); r['ack_deadline'][0] < r['ack_deadline'][1]. Extra tracing fields are ignored; validation does not mutate the record.

Why this case matters

A deterministic local contract for replication. Each negative fixture violates exactly one invariant. No transport timing, persistence, cryptographic verification, or full protocol implementation is claimed.

1 / The failure

Exit 1

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

N = 1
observations = []
def solve(r):
    return (len(set(r['distinct_replicas'][0])) >= r['distinct_replicas'][1]) and (sum(r['durable_acks'][0]) >= r['durable_acks'][1]) and (all(x == r['write_binding'][0] for x in r['write_binding'][1])) and (r['ack_deadline'][0] < r['ack_deadline'][1])
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
r = {'distinct_replicas': [['a', 'b'], 2], 'durable_acks': [[True, True, False], 2], 'failure_domains': [['z1', 'z2'], 2], 'write_binding': ['w2', ['w2', 'w2']], 'ack_deadline': [9, 10]}
check('valid operation', solve(r), True)
check('Repeated acknowledgements count as separate replicas', solve(dict(r, **{'distinct_replicas': [['a', 'a'], 2]})), False)
check('Volatile receipt acknowledgements satisfy durable concern', solve(dict(r, **{'durable_acks': [[True, False, False], 2]})), False)
check('Multiple copies in one failure domain satisfy zone concern', solve(dict(r, **{'failure_domains': [['z1', 'z1'], 2]})), False)
check('Replica acknowledgements refer to another write', solve(dict(r, **{'write_binding': ['w2', ['w1', 'w2']]})), False)
check('A write is reported successful after its response deadline', solve(dict(r, **{'ack_deadline': [10, 10]})), False)
check('unrelated tracing metadata', solve(dict(r, trace='run-'+str(N))), True)
check('repeat validation is pure', solve(r), True)
invalid = {'distinct_replicas': [['a', 'a'], 2], 'durable_acks': [[True, False, False], 2], 'failure_domains': [['z1', 'z1'], 2], 'write_binding': ['w2', ['w1', 'w2']], 'ack_deadline': [10, 10]}
keys = list(invalid)
pair = {keys[N % len(keys)]: invalid[keys[N % len(keys)]], keys[(N+1) % len(keys)]: invalid[keys[(N+1) % len(keys)]]}
check('two independent violations in variant', solve(dict(r, **pair)), False)
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
valid operation	`True`	`True`	Passed
Repeated acknowledgements count as separate replicas	`False`	`False`	Passed
Volatile receipt acknowledgements satisfy durable concern	`False`	`False`	Passed
Multiple copies in one failure domain satisfy zone concern	`True`	`False`	Failed
Replica acknowledgements refer to another write	`False`	`False`	Passed
A write is reported successful after its response deadline	`False`	`False`	Passed
unrelated tracing metadata	`True`	`True`	Passed
repeat validation is pure	`True`	`True`	Passed
two independent violations in variant	`False`	`False`	Passed

SHA-256 / 63a3d8afa6a11aa104820d45f54bf2ec3f361db669ffad658eed41d926ae00cb

2 / The unsuccessful fix

Exit 1

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

N = 1
observations = []
def solve(r):
    return (len(set(r['distinct_replicas'][0])) >= r['distinct_replicas'][1]) and (sum(r['durable_acks'][0]) >= r['durable_acks'][1]) and (len(set(r['failure_domains'][0])) >= r['failure_domains'][1]) and (r['ack_deadline'][0] < r['ack_deadline'][1])
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
r = {'distinct_replicas': [['a', 'b'], 2], 'durable_acks': [[True, True, False], 2], 'failure_domains': [['z1', 'z2'], 2], 'write_binding': ['w2', ['w2', 'w2']], 'ack_deadline': [9, 10]}
check('valid operation', solve(r), True)
check('Repeated acknowledgements count as separate replicas', solve(dict(r, **{'distinct_replicas': [['a', 'a'], 2]})), False)
check('Volatile receipt acknowledgements satisfy durable concern', solve(dict(r, **{'durable_acks': [[True, False, False], 2]})), False)
check('Multiple copies in one failure domain satisfy zone concern', solve(dict(r, **{'failure_domains': [['z1', 'z1'], 2]})), False)
check('Replica acknowledgements refer to another write', solve(dict(r, **{'write_binding': ['w2', ['w1', 'w2']]})), False)
check('A write is reported successful after its response deadline', solve(dict(r, **{'ack_deadline': [10, 10]})), False)
check('unrelated tracing metadata', solve(dict(r, trace='run-'+str(N))), True)
check('repeat validation is pure', solve(r), True)
invalid = {'distinct_replicas': [['a', 'a'], 2], 'durable_acks': [[True, False, False], 2], 'failure_domains': [['z1', 'z1'], 2], 'write_binding': ['w2', ['w1', 'w2']], 'ack_deadline': [10, 10]}
keys = list(invalid)
pair = {keys[N % len(keys)]: invalid[keys[N % len(keys)]], keys[(N+1) % len(keys)]: invalid[keys[(N+1) % len(keys)]]}
check('two independent violations in variant', solve(dict(r, **pair)), False)
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
valid operation	`True`	`True`	Passed
Repeated acknowledgements count as separate replicas	`False`	`False`	Passed
Volatile receipt acknowledgements satisfy durable concern	`False`	`False`	Passed
Multiple copies in one failure domain satisfy zone concern	`False`	`False`	Passed
Replica acknowledgements refer to another write	`True`	`False`	Failed
A write is reported successful after its response deadline	`False`	`False`	Passed
unrelated tracing metadata	`True`	`True`	Passed
repeat validation is pure	`True`	`True`	Passed
two independent violations in variant	`False`	`False`	Passed

SHA-256 / ff86455c1df88840192766cd1648cf63cdf30527b0a32292a5b26bb8e962aad8

HELD IN THE MEMBER ARCHIVE

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

This mechanism has 9 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.

Member access is invitation-based. Sign in with your invited account to inspect the repair.

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 2026-09-29T14:36:55.551263+00:00.

Case digest / c804e16704219894bc952606e7027bbb3e45556fbc15d4b636d25f9fd4ad8b3d