Celery Memory leak in Exception Task with Prefork(worker)

The Fix

pip install celery==4.4.2

Based on closed celery/celery issue #6023 · PR/commit linked

Production note: This usually shows up under retries/timeouts. Treat it as a side-effect risk until you can verify behavior with a canary + real traffic.

Jump to Verify Open PR/Commit

@@ -82,7 +82,8 @@
 
 log_policy_t = namedtuple(
-    'log_policy_t', ('format', 'description', 'severity', 'traceback', 'mail'),
+    'log_policy_t',
+    ('format', 'description', 'severity', 'traceback', 'mail'),

repro

this bug.

verify

Follow the reproduction steps, confirm the failure, apply the fix, and repeat the same steps to verify the behavior changes.

fix.md

Option A — Upgrade to fixed release\npip install celery==4.4.2\nWhen NOT to use: This fix should not be applied if the application relies on the previous traceback behavior for debugging.\n\n

Why This Fix Works in Production

Trigger: Memory leak in Exception Task with Prefork(worker)
Mechanism: A memory leak occurs due to a frame reference in exception handling not being cleaned up properly
Why the fix works: Addresses a memory leak issue in the Exception Task with Prefork by cleaning up the traceback. (first fixed release: 4.4.2).

Why This Breaks in Prod

A memory leak occurs due to a frame reference in exception handling not being cleaned up properly
Production symptom (often without a traceback): Memory leak in Exception Task with Prefork(worker)

Proof / Evidence

GitHub issue: #6023
Fix PR: https://github.com/celery/celery/pull/6024
First fixed release: 4.4.2
Reproduced locally: No (not executed)
Last verified: 2026-02-09
Confidence: 0.85
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.80

Discussion

High-signal excerpts from the issue thread (symptoms, repros, edge-cases).

Jump to Sources Open on GitHub

“ # Checklist  - [x] I hav”

Issue thread · issue description · source

Failure Signature (Search String)

Memory leak in Exception Task with Prefork(worker)
- [x] I have included all related issues and possible duplicate issues

Copy-friendly signature

signature.txt

Failure Signature
-----------------
Memory leak  in Exception Task with Prefork(worker)
- [x] I have included all related issues and possible duplicate issues

Error Message

Signature-only (no traceback captured)

error.txt

Error Message
-------------
Memory leak  in Exception Task with Prefork(worker)
- [x] I have included all related issues and possible duplicate issues

Minimal Reproduction

this bug.

What Broke

The application experiences increased memory usage leading to potential crashes or slowdowns.

Why It Broke

A memory leak occurs due to a frame reference in exception handling not being cleaned up properly

Fix Options (Details)

Option A — Upgrade to fixed release Safe default (recommended)

pip install celery==4.4.2

When NOT to use: This fix should not be applied if the application relies on the previous traceback behavior for debugging.

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.

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)

See OnceOnly SDK

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/6024

First fixed release: 4.4.2

Last verified: 2026-02-09. Validate in your environment.

When NOT to Use This Fix

This fix should not be applied if the application relies on the previous traceback behavior for debugging.
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

Follow the reproduction steps, confirm the failure, apply the fix, and repeat the same steps to verify the behavior changes.

Did This Fix Work in Your Case?

Quick signal helps us prioritize which fixes to verify and improve.

Prevention

Track RSS + object counts after deployments; alert on monotonic growth and GC pressure.
Add a long-running test that repeats the failing call path and asserts stable memory.

Version Compatibility Table

Version	Status
4.4.2	Fixed

Related Issues

No related fixes found.

Cluster: celery:memory-leak Celery hub Celery best practices All hubs All clusters

Related clusters: Configuration error Data consistency Duplicates

Sources

We don’t republish the full GitHub discussion text. Use the links above for context.

Celery Memory leak in Exception Task with Prefork(worker) (Fix)