FA-1461 / Concurrency / Open access

Commit a two-phase transaction: Commit messages precede the durable coordinator decision · case 01

The distributed transaction operation is admitted even though commit messages precede the durable coordinator decision.

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

ROOT CAUSE

The admission path omits the decision durable invariant while validating the other operation preconditions.

VERIFIED REPAIR

Require r['decision_durable'] is True together with every other stated precondition before accepting the operation.

Unsuccessful approach: Adding the decision durable check repairs the reported defect, but replacing the adjacent participant set check loses that independent invariant.

Case contract

Return a Boolean admission decision for commit a two-phase transaction. The record r must satisfy all of: all(x == 'prepared' for x in r['all_prepared']); 'abort' not in r['no_abort_vote']; r['decision_durable'] is True; set(r['participant_set'][0]) == set(r['participant_set'][1]); r['coordinator_epoch'][0] == r['coordinator_epoch'][1]. Extra tracing fields are ignored; validation does not mutate the record.

Why this case matters

A deterministic local contract for concurrency. 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 (all(x == 'prepared' for x in r['all_prepared'])) and ('abort' not in r['no_abort_vote']) and (set(r['participant_set'][0]) == set(r['participant_set'][1])) and (r['coordinator_epoch'][0] == r['coordinator_epoch'][1])
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
r = {'all_prepared': ['prepared', 'prepared'], 'no_abort_vote': ['yes', 'yes'], 'decision_durable': True, 'participant_set': [['a', 'b'], ['a', 'b']], 'coordinator_epoch': [5, 5]}
check('valid operation', solve(r), True)
check('Commit proceeds while a participant has not prepared', solve(dict(r, **{'all_prepared': ['prepared', 'working']})), False)
check('A participant abort vote is ignored', solve(dict(r, **{'no_abort_vote': ['yes', 'abort']})), False)
check('Commit messages precede the durable coordinator decision', solve(dict(r, **{'decision_durable': False})), False)
check('A newly enlisted participant is omitted from the decision', solve(dict(r, **{'participant_set': [['a', 'b'], ['a']]})), False)
check('A recovered coordinator accepts the prior instance decision', solve(dict(r, **{'coordinator_epoch': [4, 5]})), False)
check('unrelated tracing metadata', solve(dict(r, trace='run-'+str(N))), True)
check('repeat validation is pure', solve(r), True)
invalid = {'all_prepared': ['prepared', 'working'], 'no_abort_vote': ['yes', 'abort'], 'decision_durable': False, 'participant_set': [['a', 'b'], ['a']], 'coordinator_epoch': [4, 5]}
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
Commit proceeds while a participant has not prepared	`False`	`False`	Passed
A participant abort vote is ignored	`False`	`False`	Passed
Commit messages precede the durable coordinator decision	`True`	`False`	Failed
A newly enlisted participant is omitted from the decision	`False`	`False`	Passed
A recovered coordinator accepts the prior instance decision	`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 / ffc67acbeabaf56721aa7ef1c2217cc6e05918097716f1887daa8f65cd3a1159

2 / The unsuccessful fix

Exit 1

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

N = 1
observations = []
def solve(r):
    return (all(x == 'prepared' for x in r['all_prepared'])) and ('abort' not in r['no_abort_vote']) and (r['decision_durable'] is True) and (r['coordinator_epoch'][0] == r['coordinator_epoch'][1])
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
r = {'all_prepared': ['prepared', 'prepared'], 'no_abort_vote': ['yes', 'yes'], 'decision_durable': True, 'participant_set': [['a', 'b'], ['a', 'b']], 'coordinator_epoch': [5, 5]}
check('valid operation', solve(r), True)
check('Commit proceeds while a participant has not prepared', solve(dict(r, **{'all_prepared': ['prepared', 'working']})), False)
check('A participant abort vote is ignored', solve(dict(r, **{'no_abort_vote': ['yes', 'abort']})), False)
check('Commit messages precede the durable coordinator decision', solve(dict(r, **{'decision_durable': False})), False)
check('A newly enlisted participant is omitted from the decision', solve(dict(r, **{'participant_set': [['a', 'b'], ['a']]})), False)
check('A recovered coordinator accepts the prior instance decision', solve(dict(r, **{'coordinator_epoch': [4, 5]})), False)
check('unrelated tracing metadata', solve(dict(r, trace='run-'+str(N))), True)
check('repeat validation is pure', solve(r), True)
invalid = {'all_prepared': ['prepared', 'working'], 'no_abort_vote': ['yes', 'abort'], 'decision_durable': False, 'participant_set': [['a', 'b'], ['a']], 'coordinator_epoch': [4, 5]}
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
Commit proceeds while a participant has not prepared	`False`	`False`	Passed
A participant abort vote is ignored	`False`	`False`	Passed
Commit messages precede the durable coordinator decision	`False`	`False`	Passed
A newly enlisted participant is omitted from the decision	`True`	`False`	Failed
A recovered coordinator accepts the prior instance decision	`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 / 0f55dc2beff71a9b74690eeb4053848bfe4d64ace9f616b55968fcbfa43c5865

3 / The verified repair

Exit 0

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

N = 1
observations = []
def solve(r):
    return (all(x == 'prepared' for x in r['all_prepared'])) and ('abort' not in r['no_abort_vote']) and (r['decision_durable'] is True) and (set(r['participant_set'][0]) == set(r['participant_set'][1])) and (r['coordinator_epoch'][0] == r['coordinator_epoch'][1])
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
r = {'all_prepared': ['prepared', 'prepared'], 'no_abort_vote': ['yes', 'yes'], 'decision_durable': True, 'participant_set': [['a', 'b'], ['a', 'b']], 'coordinator_epoch': [5, 5]}
check('valid operation', solve(r), True)
check('Commit proceeds while a participant has not prepared', solve(dict(r, **{'all_prepared': ['prepared', 'working']})), False)
check('A participant abort vote is ignored', solve(dict(r, **{'no_abort_vote': ['yes', 'abort']})), False)
check('Commit messages precede the durable coordinator decision', solve(dict(r, **{'decision_durable': False})), False)
check('A newly enlisted participant is omitted from the decision', solve(dict(r, **{'participant_set': [['a', 'b'], ['a']]})), False)
check('A recovered coordinator accepts the prior instance decision', solve(dict(r, **{'coordinator_epoch': [4, 5]})), False)
check('unrelated tracing metadata', solve(dict(r, trace='run-'+str(N))), True)
check('repeat validation is pure', solve(r), True)
invalid = {'all_prepared': ['prepared', 'working'], 'no_abort_vote': ['yes', 'abort'], 'decision_durable': False, 'participant_set': [['a', 'b'], ['a']], 'coordinator_epoch': [4, 5]}
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
Commit proceeds while a participant has not prepared	`False`	`False`	Passed
A participant abort vote is ignored	`False`	`False`	Passed
Commit messages precede the durable coordinator decision	`False`	`False`	Passed
A newly enlisted participant is omitted from the decision	`False`	`False`	Passed
A recovered coordinator accepts the prior instance decision	`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 / 94e1a49da4a6a7d3f634fc190726bb5ed57954c5c46cf0ab258b7cacc624f2ab

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 2026-09-29T14:37:02.417793+00:00.

Case digest / 7d2508fa28371655b144dc1b7e2fa59f431123ffbd2d51745cc80cafd2967977