urllib3 Performance issue in `BytesQueueBuffer.get()` byte

The Fix

pip install urllib3==2.6.0

Based on closed urllib3/urllib3 issue #3710 · PR/commit linked

Jump to Verify Open PR/Commit

@@ -0,0 +1 @@
@@ -0,0 +1 @@
+Improved the performance of content decoding by optimizing ``BytesQueueBuffer`` class.
diff --git a/src/urllib3/response.py b/src/urllib3/response.py
index d427e7148d..3df98184de 100644

repro.py

from compression import zstd
import io
import timeit

from urllib3.response import HTTPResponse


data = b"A" * (1024 * 1024 * 1024)  # 1 GB
compressed_data = zstd.ZstdCompressor().compress(data)


def decompress():
    fp = io.BytesIO(compressed_data)
    r = HTTPResponse(fp, headers={"content-encoding": "zstd"}, preload_content=False)
    while r.read(32 * 1024):
        pass

time_taken = timeit.timeit(decompress, number=10)
print(f"Decompression time: {time_taken:.2f} seconds")

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 urllib3==2.6.0\nWhen NOT to use: This fix should not be used if backward compatibility with older versions is required.\n\n

Why This Fix Works in Production

Trigger: OpenSSL 3.0.14 4 Jun 2024
Mechanism: Improves the speed of `BytesQueueBuffer.get()` by using memoryview, solving the problem described in #3710.
Why the fix works: Improves the speed of `BytesQueueBuffer.get()` by using memoryview, solving the problem described in #3710. (first fixed release: 2.6.0).

Why This Breaks in Prod

Shows up under Python 3.12.5 in real deployments (not just unit tests).
Production symptom (often without a traceback): OpenSSL 3.0.14 4 Jun 2024

Proof / Evidence

GitHub issue: #3710
Fix PR: https://github.com/urllib3/urllib3/pull/3711
First fixed release: 2.6.0
Reproduced locally: No (not executed)
Last verified: 2026-02-09
Confidence: 0.85
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.60

Discussion

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

Jump to Sources Open on GitHub

“FYI, we did further improvements in c19571de34c47de3a766541b041637ba5f716ed7”

@illia-v · 2025-12-05 · source

Failure Signature (Search String)

OpenSSL 3.0.14 4 Jun 2024
CPU: 13th Gen Intel(R) Core(TM) i5-13500

Copy-friendly signature

signature.txt

Failure Signature
-----------------
OpenSSL 3.0.14 4 Jun 2024
CPU: 13th Gen Intel(R) Core(TM) i5-13500

Error Message

Signature-only (no traceback captured)

error.txt

Error Message
-------------
OpenSSL 3.0.14 4 Jun 2024
CPU: 13th Gen Intel(R) Core(TM) i5-13500

Minimal Reproduction

repro.py

from compression import zstd
import io
import timeit

from urllib3.response import HTTPResponse


data = b"A" * (1024 * 1024 * 1024)  # 1 GB
compressed_data = zstd.ZstdCompressor().compress(data)


def decompress():
    fp = io.BytesIO(compressed_data)
    r = HTTPResponse(fp, headers={"content-encoding": "zstd"}, preload_content=False)
    while r.read(32 * 1024):
        pass

time_taken = timeit.timeit(decompress, number=10)
print(f"Decompression time: {time_taken:.2f} seconds")

Environment

Python: 3.12.5
urllib3: 0.1

What Broke

Content retrieval time was significantly slower when decoding gzipped data.

Fix Options (Details)

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

pip install urllib3==2.6.0

When NOT to use: This fix should not be used if backward compatibility with older versions is required.

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

Fix reference: https://github.com/urllib3/urllib3/pull/3711

First fixed release: 2.6.0

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

When NOT to Use This Fix

This fix should not be used if backward compatibility with older versions is required.

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

Add a CI check that diffs key outputs after upgrades (OpenAPI schema snapshots, JSON payload shapes, CLI output).
Upgrade behind a canary and run integration tests against the canary before 100% rollout.
Add a TLS smoke test that performs a real handshake in CI (include CA bundle validation and hostname checks).
Alert on handshake failures by error string and endpoint to catch cert/CA changes quickly.

Version Compatibility Table

Version	Status
2.6.0	Fixed

Related Issues

No related fixes found.

Cluster: urllib3:ssl-handshake urllib3 hub urllib3 best practices All hubs All clusters

Related clusters: Configuration error Data consistency Other

Sources

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

urllib3 Performance issue in `BytesQueueBuffer.get()` byte slicing (Fix)