Celery What type of pool is created for redis broker (Fix)

The Fix

pip install celery==4.4.0rc5

Based on closed celery/celery issue #5567 · 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.

Open PR/Commit

@@ -1052,6 +1052,10 @@ Default: No limit.
 pool used for sending and retrieving results.
 
+.. warning::
+    Redis will raise a `ConnectionError` if the number of concurrent
+    connections exceeds the maximum.

fix.md

Option A — Upgrade to fixed release\npip install celery==4.4.0rc5\nWhen NOT to use: This fix is not applicable if the documentation does not require clarification on connection limits.\n\n

Why This Fix Works in Production

Trigger: - [x] I have included all related issues and possible duplicate issues in this issue
Mechanism: The documentation did not clarify the behavior of Redis connection limits
Why the fix works: Adds a warning to the documentation regarding the `max_redis_connections` setting, indicating that exceeding the maximum number of concurrent connections will raise a `ConnectionError`. (first fixed release: 4.4.0rc5).

Production impact:

If left unfixed, the same config can fail only in production (env differences), causing startup failures or partial feature outages.

Why This Breaks in Prod

The documentation did not clarify the behavior of Redis connection limits
Production symptom (often without a traceback): - [x] I have included all related issues and possible duplicate issues in this issue

Proof / Evidence

GitHub issue: #5567
Fix PR: https://github.com/celery/celery/pull/5618
First fixed release: 4.4.0rc5
Reproduced locally: No (not executed)
Last verified: 2026-02-09
Confidence: 0.85
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.72

Discussion

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

Jump to Sources Open on GitHub

“can you create a pr for docs improvement?”

@auvipy · 2019-06-07 · source

“@okomarov I'm using celery with redis as broker & backend”

@SBhat2615 · 2025-03-05 · source

“@auvipy I will add some clarifications to the redis_max_connections setting which will partially solve the issue above”

@okomarov · 2019-06-11 · source

Failure Signature (Search String)

- [x] I have included all related issues and possible duplicate issues in this issue
In contrast, the [`redis.connection.BlockingConnectionPool`](https://redis-py.readthedocs.io/en/latest/#redis.BlockingConnectionPool) does not raise an error and waits until a

Copy-friendly signature

signature.txt

Failure Signature
-----------------
- [x] I have included all related issues and possible duplicate issues in this issue
In contrast, the [`redis.connection.BlockingConnectionPool`](https://redis-py.readthedocs.io/en/latest/#redis.BlockingConnectionPool) does not raise an error and waits until a connection becomes available in the pool.

Error Message

Signature-only (no traceback captured)

error.txt

Error Message
-------------
- [x] I have included all related issues and possible duplicate issues in this issue
In contrast, the [`redis.connection.BlockingConnectionPool`](https://redis-py.readthedocs.io/en/latest/#redis.BlockingConnectionPool) does not raise an error and waits until a connection becomes available in the pool.

What Broke

Users may experience connection errors when exceeding Redis connection limits.

Why It Broke

The documentation did not clarify the behavior of Redis connection limits

Fix Options (Details)

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

pip install celery==4.4.0rc5

When NOT to use: This fix is not applicable if the documentation does not require clarification on connection limits.

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/5618

First fixed release: 4.4.0rc5

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

When NOT to Use This Fix

This fix is not applicable if the documentation does not require clarification on connection limits.

Did This Fix Work in Your Case?

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

Prevention

Add a stress test that runs high-concurrency workloads and fails on thread dumps / blocked locks.
Enable watchdog dumps in prod (faulthandler, thread dump endpoint) to capture deadlocks quickly.
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
4.4.0rc5	Fixed

Related Issues

No related fixes found.

Cluster: celery:configuration-error Celery hub Celery best practices All hubs All clusters

Related clusters: Data consistency Duplicates Duplicate processing

Sources

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