Celery Group results aren't cleaned up on result.forget() -

The Fix

pip install celery==5.6.0

Based on closed celery/celery issue #9797 · 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

@@ -137,6 +137,8 @@ def forget(self):
         if self.parent:
             self.parent.forget()
+
+        self.backend.remove_pending_result(self)
         self.backend.forget(self.id)

repro.py

aiomqtt==2.4.0
amqp==5.3.1
annotated-types==0.7.0
anyio==4.9.0
billiard==4.2.1
celery==5.5.3
celery-types==0.23.0
certifi==2025.6.15
charset-normalizer==3.4.2
click==8.2.1
click-didyoumean==0.3.1
click-plugins==1.1.1.2
click-repl==0.3.0
debugpy==1.8.14
dnspython==2.7.0
docker==7.1.0
email_validator==2.2.0
fastapi==0.115.14
fastapi-cli==0.0.7
h11==0.16.0
httpcore==1.0.9
httptools==0.6.4
httpx==0.28.1
idna==3.10
influxdb==5.3.2
iniconfig==2.1.0
Jinja2==3.1.6
kombu==5.5.4
linkify-it-py==2.0.3
markdown-it-py==3.0.0
MarkupSafe==3.0.2
mdit-py-plugins==0.4.2
mdurl==0.1.2
memray==1.17.2
more-itertools==10.7.0
msgpack==1.1.1
packaging==25.0
paho-mqtt==2.1.0
platformdirs==4.3.8
pluggy==1.6.0
prompt_toolkit==3.0.51
psutil==7.0.0
pydantic==2.11.7
pydantic-settings==2.10.1
pydantic_core==2.33.2
Pygments==2.19.2
pytest==8.4.1
pytest-celery==1.2.0
pytest_docker_tools==3.1.9
python-dateutil==2.9.0.post0
python-dotenv==1.1.1
python-multipart==0.0.20
pytz==2025.2
PyYAML==6.0.2
redis==5.2.1
requests==2.32.4
rich==14.0.0
rich-toolkit==0.14.7
ruff==0.12.2
setuptools==80.9.0
shellingham==1.5.4
six==1.17.0
sniffio==1.3.1
starlette==0.46.2
structlog==25.4.0
tenacity==9.1.2
textual==3.5.0
typer==0.16.0
typing-inspection==0.4.1
typing_extensions==4.14.0
tzdata==2025.2
uc-micro-py==1.0.3
urllib3==2.5.0
uvicorn==0.34.3
uvloop==0.21.0
vine==5.1.0
watchfiles==1.1.0
wcwidth==0.2.13
websockets==15.0.1

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==5.6.0\nWhen NOT to use: This fix should not be applied if the application relies on retaining task results.\n\n

Why This Fix Works in Production

Trigger: Group results aren't cleaned up on result.forget() - memory leak
Mechanism: Subscriptions are not cleaned up when forget is called, leading to memory leaks
Why the fix works: Fixes a memory leak caused by subscriptions not being cleaned up when forget is called. (first fixed release: 5.6.0).

Production impact:

If left unfixed, this can cause silent data inconsistencies that propagate (bad cache entries, incorrect downstream decisions).

Why This Breaks in Prod

Shows up under Python 3.13 in real deployments (not just unit tests).
Subscriptions are not cleaned up when forget is called, leading to memory leaks
Production symptom (often without a traceback): Group results aren't cleaned up on result.forget() - memory leak

Proof / Evidence

GitHub issue: #9797
Fix PR: https://github.com/celery/celery/pull/9806
First fixed release: 5.6.0
Reproduced locally: No (not executed)
Last verified: 2026-02-09
Confidence: 0.75
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.43

Discussion

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

Jump to Sources Open on GitHub

“you can check this PR and use the idea to help reproduce it using integration tests https://github.com/celery/celery/pull/9799”

@auvipy · 2025-07-06 · source

“do we really needed a duplicate new issue?”

@auvipy · 2025-07-05 · source

“> do we really needed a duplicate new issue? Good point”

@tsoos99dev · 2025-07-05 · source

“I'll do that. Groups aren't usable right now. I did some more tests with calling get, and the pending task object is only cleared if…”

@tsoos99dev · 2025-07-06 · source

Failure Signature (Search String)

Group results aren't cleaned up on result.forget() - memory leak
- [x] I have included all related issues and possible duplicate issues

Copy-friendly signature

signature.txt

Failure Signature
-----------------
Group results aren't cleaned up on result.forget() - memory leak
- [x] I have included all related issues and possible duplicate issues

Error Message

Signature-only (no traceback captured)

error.txt

Error Message
-------------
Group results aren't cleaned up on result.forget() - memory leak
- [x] I have included all related issues and possible duplicate issues

Minimal Reproduction

repro.py

aiomqtt==2.4.0
amqp==5.3.1
annotated-types==0.7.0
anyio==4.9.0
billiard==4.2.1
celery==5.5.3
celery-types==0.23.0
certifi==2025.6.15
charset-normalizer==3.4.2
click==8.2.1
click-didyoumean==0.3.1
click-plugins==1.1.1.2
click-repl==0.3.0
debugpy==1.8.14
dnspython==2.7.0
docker==7.1.0
email_validator==2.2.0
fastapi==0.115.14
fastapi-cli==0.0.7
h11==0.16.0
httpcore==1.0.9
httptools==0.6.4
httpx==0.28.1
idna==3.10
influxdb==5.3.2
iniconfig==2.1.0
Jinja2==3.1.6
kombu==5.5.4
linkify-it-py==2.0.3
markdown-it-py==3.0.0
MarkupSafe==3.0.2
mdit-py-plugins==0.4.2
mdurl==0.1.2
memray==1.17.2
more-itertools==10.7.0
msgpack==1.1.1
packaging==25.0
paho-mqtt==2.1.0
platformdirs==4.3.8
pluggy==1.6.0
prompt_toolkit==3.0.51
psutil==7.0.0
pydantic==2.11.7
pydantic-settings==2.10.1
pydantic_core==2.33.2
Pygments==2.19.2
pytest==8.4.1
pytest-celery==1.2.0
pytest_docker_tools==3.1.9
python-dateutil==2.9.0.post0
python-dotenv==1.1.1
python-multipart==0.0.20
pytz==2025.2
PyYAML==6.0.2
redis==5.2.1
requests==2.32.4
rich==14.0.0
rich-toolkit==0.14.7
ruff==0.12.2
setuptools==80.9.0
shellingham==1.5.4
six==1.17.0
sniffio==1.3.1
starlette==0.46.2
structlog==25.4.0
tenacity==9.1.2
textual==3.5.0
typer==0.16.0
typing-inspection==0.4.1
typing_extensions==4.14.0
tzdata==2025.2
uc-micro-py==1.0.3
urllib3==2.5.0
uvicorn==0.34.3
uvloop==0.21.0
vine==5.1.0
watchfiles==1.1.0
wcwidth==0.2.13
websockets==15.0.1

Environment

Python: 3.13

What Broke

Memory usage grows indefinitely due to uncleaned subscriptions after task completion.

Why It Broke

Subscriptions are not cleaned up when forget is called, leading to memory leaks

Fix Options (Details)

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

pip install celery==5.6.0

When NOT to use: This fix should not be applied if the application relies on retaining task results.

Use when you can deploy the upstream fix. It is usually lower-risk than long-lived workarounds.

Fix reference: https://github.com/celery/celery/pull/9806

First fixed release: 5.6.0

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 retaining task results.

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

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
5.6.0	Fixed

Related Issues

No related fixes found.

Cluster: celery:data-consistency Celery hub Celery best practices All hubs All clusters

Related clusters: Configuration error Duplicates Duplicate processing

Sources

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

Celery Group results aren't cleaned up on result.forget() - memory leak (Fix)