The Fix
pip install celery==4.4.7
Based on closed celery/celery issue #6256 · PR/commit linked
@@ -630,7 +630,7 @@ def test_add_chord_to_chord(self, manager):
c = group([add_chord_to_chord.s([1, 2, 3], 4)]) | identity.s()
res = c()
- assert res.get() == [0, 5 + 6 + 7]
+ assert sorted(res.get()) == [0, 5 + 6 + 7]
repro.py
@pytest.mark.flaky(reruns=5, reruns_delay=1, cause=is_retryable_exception)
def test_add_chord_to_chord(self, manager):
if not manager.app.conf.result_backend.startswith('redis'):
raise pytest.skip('Requires redis result backend.')
verify
Re-run the minimal reproduction on your broken version, then apply the fix and re-run.
fix.md
Option A — Upgrade to fixed release\npip install celery==4.4.7\nWhen NOT to use: Do not use this fix if the order of results is significant for your application logic.\n\n
Why This Fix Works in Production
- Trigger: t/integration/test_canvas.py:630: AssertionError
- Mechanism: The test failed due to an ordering issue in the result comparison
- Why the fix works: Fixes a flaky test by ensuring the result is sorted before comparison. (first fixed release: 4.4.7).
Production impact:
- If left unfixed, this can cause silent data inconsistencies that propagate (bad cache entries, incorrect downstream decisions).
Why This Breaks in Prod
- The test failed due to an ordering issue in the result comparison
- Surfaces as: ―――――――――――――――――――――― test_chord.test_add_chord_to_chord ――――――――――――――――――――――
Proof / Evidence
- GitHub issue: #6256
- Fix PR: https://github.com/celery/celery/pull/6263
- First fixed release: 4.4.7
- Reproduced locally: No (not executed)
- Last verified: 2026-02-09
- Confidence: 0.85
- Did this fix it?: Yes (upstream fix exists)
- Own content ratio: 0.42
Discussion
High-signal excerpts from the issue thread (symptoms, repros, edge-cases).
“seems some ordering issue?”
Failure Signature (Search String)
- t/integration/test_canvas.py:630: AssertionError
Error Message
Stack trace
error.txt
Error Message
-------------
―――――――――――――――――――――― test_chord.test_add_chord_to_chord ――――――――――――――――――――――
self = <t.integration.test_canvas.test_chord object at 0x7fd694409220>
manager = <celery.contrib.testing.manager.Manager object at 0x7fd6944093a0>
@pytest.mark.flaky(reruns=5, reruns_delay=1, cause=is_retryable_exception)
def test_add_chord_to_chord(self, manager):
if not manager.app.conf.result_backend.startswith('redis'):
raise pytest.skip('Requires redis result backend.')
c = group([add_chord_to_chord.s([1, 2, 3], 4)]) | identity.s()
res = c()
assert res.get() == [0, 5 + 6 + 7]
E assert [18, 0] == [0, 18]
E At index 0 diff: 18 != 0
E Full diff:
E - [18, 0]
E + [0, 18]
t/integration/test_canvas.py:630: AssertionError
------------------------------ Captured log call -------------------------------
Minimal Reproduction
repro.py
@pytest.mark.flaky(reruns=5, reruns_delay=1, cause=is_retryable_exception)
def test_add_chord_to_chord(self, manager):
if not manager.app.conf.result_backend.startswith('redis'):
raise pytest.skip('Requires redis result backend.')
Why It Broke
The test failed due to an ordering issue in the result comparison
Fix Options (Details)
Option A — Upgrade to fixed release Safe default (recommended)
pip install celery==4.4.7
When NOT to use: Do not use this fix if the order of results is significant for your application logic.
Use when you can deploy the upstream fix. It is usually lower-risk than long-lived workarounds.
Option D — Guard side-effects with OnceOnly Guardrail for side-effects
Mitigate duplicate external side-effects under retries/timeouts/agent loops by gating the operation before calling external systems.
- Place OnceOnly between your code/agent and real side-effects (Stripe, emails, CRM, APIs).
- Use a stable key per side-effect (e.g., customer_id + action + idempotency_key).
- Fail-safe: configure fail-open vs fail-closed based on blast radius and spend risk.
- This does NOT fix data corruption; it only prevents duplicate side-effects.
Show example snippet (optional)
onceonly.py
from onceonly import OnceOnly
import os
once = OnceOnly(api_key=os.environ["ONCEONLY_API_KEY"], fail_open=True)
# Stable idempotency key per real side-effect.
# Use a request id / job id / webhook delivery id / Stripe event id, etc.
event_id = "evt_..." # replace
key = f"stripe:webhook:{event_id}"
res = once.check_lock(key=key, ttl=3600)
if res.duplicate:
return {"status": "already_processed"}
# Safe to execute the side-effect exactly once.
handle_event(event_id)
When NOT to use: Do not use this to hide logic bugs or data corruption. Use it to block duplicate external side-effects and enforce tool permissions/spend caps.
Fix reference: https://github.com/celery/celery/pull/6263
First fixed release: 4.4.7
Last verified: 2026-02-09. Validate in your environment.
When NOT to Use This Fix
- Do not use this fix if the order of results is significant for your application logic.
- Do not use this to hide logic bugs or data corruption. Use it to block duplicate external side-effects and enforce tool permissions/spend caps.
Verify Fix
verify
Re-run the minimal reproduction on your broken version, then apply the fix and re-run.
Did This Fix Work in Your Case?
Quick signal helps us prioritize which fixes to verify and improve.
Prevention
- Capture the exact failing error string in logs and tests so you can reproduce via a minimal script.
- Pin production dependencies and upgrade only with a reproducible test that hits the failing path.
Version Compatibility Table
| Version | Status |
|---|---|
| 4.4.7 | Fixed |
Related Issues
No related fixes found.
Sources
We don’t republish the full GitHub discussion text. Use the links above for context.