gh-150818: Speed up logging.getLogger() for existing loggers (GH-150825) by gaborbernat · Pull Request #150825 · python/cpython · GitHub

logging.getLogger(name) returns the singleton logger for a name, creating it on first use. Every call takes the logging lock, even the overwhelmingly common case where the logger already exists and is returned unchanged. Libraries fetch their logger by name throughout their code, at module import and again inside functions, so the same handful of names are looked up over and over for the life of a process. Those repeat lookups are pure overhead: the logger is already there.

This returns an existing, fully-initialised logger through a lock-free fast path before falling back to the locked section. The fast path reads loggerDict with a single dict.get(), which is atomic under both the GIL and free threading, and a Logger is inserted into that dict only after it is fully constructed under the lock, so the fast path never observes a half-built object or a placeholder. First-time creation, placeholder resolution and the parent/child wiring still run under the lock exactly as before.

Resolving logger names collected from the top-1000 corpus improves from 6.68 µs to 5.02 µs, 33% faster.

Benchmark	base	patched
getLogger, existing loggers	6.68 µs	5.02 µs: 33% faster

Benchmark (pyperf)

Run base vs patched by swapping Lib/logging/__init__.py on the same interpreter. The names are real getLogger() string arguments mined from the top-1000 corpus.

import logging, pyperf

names = ["elastic_transport.transport", "peewee.pool", "LiteLLM", "httpx",
    "uvicorn.error", "uvicorn.access", "fsspec", "boto3", "posthog", "amqp",
    "nox", "tldextract.cache", "dulwich.lfs", "urllib3.connectionpool",
    "asyncio", "sqlalchemy.engine", "werkzeug", "django.request", "celery.worker",
    "kafka.conn", "redis.client", "paramiko.transport", "matplotlib.font_manager"]
for n in names:
    logging.getLogger(n)   # pre-create, as modules do at import

runner = pyperf.Runner()
runner.bench_func("getLogger %d existing loggers" % len(names),
                  lambda: [logging.getLogger(n) for n in names])

Resolves #150818.

Issue: Speed up logging.getLogger() for already-registered loggers #150818

getLogger() took the logging lock on every call, including the common case of an already-registered logger. Return that logger through a lock-free fast path backed by an atomic dict lookup. First-time creation, placeholder resolution and parent/child wiring still run under the lock, and the fast path is safe under both the GIL and free threading.

Both branches inside the lock assign rv before it is read, so the reset is dead code.

🤖 New build scheduled with the buildbot fleet by @vsajip for commit efad324 🤖

Results will be shown at:

https://buildbot.python.org/all/#/grid?branch=refs%2Fpull%2F150825%2Fmerge

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Thanks @gaborbernat for the PR, and @vsajip for merging it 🌮🎉.. I'm working now to backport this PR to: 3.13.
🐍🍒⛏🤖 I'm not a witch! I'm not a witch!

Thanks @gaborbernat for the PR, and @vsajip for merging it 🌮🎉.. I'm working now to backport this PR to: 3.14.
🐍🍒⛏🤖

Thanks @gaborbernat for the PR, and @vsajip for merging it 🌮🎉.. I'm working now to backport this PR to: 3.15.
🐍🍒⛏🤖

GH-150927 is a backport of this pull request to the 3.13 branch.

GH-150928 is a backport of this pull request to the 3.14 branch.

GH-150929 is a backport of this pull request to the 3.15 branch.

We don't usually backport features?

Is performance improvements a feature? 🤔

@StanFromIreland As there is no API change, I've assumed it would be OK to back-port so that earlier versions get the benefit too. Is there some precedent for not doing that?

I see that the issue was marked as a feature, by which I suppose it meant that it wasn't a bug. But it's not a feature in the sense of an API enhancement or fix.

As documented in the devguide:

The only changes allowed to occur in a maintenance branch without debate are bug fixes, test improvements, and edits to the documentation.

And also:

The only branch that receives new features is main

Neither of those places elaborate on the reasoning for this, but I think it is largely to avoid introducing any possible regressions, i.e., to preserve backwards compatibility.

I've raised a discussion topic as that same para in the devguide says

only rare exceptions are accepted and must be discussed first.

self._fixupParents(rv) is called after self.loggerDict[name] = rv.
Therefore, it is possible to get a logger whose logger.parent has not yet been set.

…ythonGH-150825)

gaborbernat requested a review from vsajip as a code owner June 2, 2026 23:29

bedevere-app Bot added the awaiting review label Jun 2, 2026

bedevere-app Bot mentioned this pull request Jun 2, 2026

Speed up logging.getLogger() for already-registered loggers #150818

Closed

gaborbernat force-pushed the opt/logging-getlogger-fastpath branch from defd276 to 9c0df96 Compare June 2, 2026 23:45

sobolevn reviewed Jun 3, 2026

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Comment thread Lib/logging/__init__.py Outdated

Drop the unused rv = None initialization

efad324

Both branches inside the lock assign rv before it is read, so the reset is dead code.

gaborbernat requested a review from sobolevn June 3, 2026 14:42

vsajip approved these changes Jun 3, 2026

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bedevere-app Bot added awaiting merge and removed awaiting review labels Jun 3, 2026

vsajip added the 🔨 test-with-buildbots Test PR w/ buildbots; report in status section label Jun 3, 2026

bedevere-bot removed the 🔨 test-with-buildbots Test PR w/ buildbots; report in status section label Jun 3, 2026

vsajip changed the title gh-150818: Speed up logging.getLogger() for existing loggers gh-150818: Speed up logging.getLogger() for existing loggers (GH-150825) Jun 4, 2026

vsajip merged commit e833f57 into python:main Jun 4, 2026
138 of 152 checks passed

bedevere-app Bot removed the awaiting merge label Jun 4, 2026

vsajip added needs backport to 3.13 only security fixes needs backport to 3.14 bugs and security fixes needs backport to 3.15 bugs and security fixes labels Jun 4, 2026

bedevere-app Bot removed the needs backport to 3.13 only security fixes label Jun 4, 2026

bedevere-app Bot removed the needs backport to 3.14 bugs and security fixes label Jun 4, 2026

bedevere-app Bot removed the needs backport to 3.15 bugs and security fixes label Jun 4, 2026

methane reviewed Jun 5, 2026

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gaborbernat mentioned this pull request Jun 5, 2026

gh-150818: Wire logger parent before publishing it in getLogger() (GH-150941) #150941

Merged

philthompson10 pushed a commit to philthompson10/cpython that referenced this pull request Jun 17, 2026

pythongh-150818 : Speed up logging.getLogger() for existing loggers (p…

2f8edef

…ythonGH-150825)

gaborbernat deleted the opt/logging-getlogger-fastpath branch October 3, 2026 15:12

+                      # returned without taking the lock. dict.get() is atomic under both
+                      # the GIL and free threading, and a Logger is fully initialised before
+                      # being inserted into loggerDict under the lock, so this never sees a
+                      # partially-constructed object.

gh-150818: Speed up logging.getLogger() for existing loggers (GH-150825) by gaborbernat · Pull Request #150825 · python/cpython · GitHub

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gh-150818: Speed up logging.getLogger() for existing loggers (GH-150825)#150825vsajip merged 2 commits intopython:mainpython/cpython:mainfrom gaborbernat:opt/logging-getlogger-fastpathgaborbernat/cpython:opt/logging-getlogger-fastpathCopy head branch name to clipboard

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gh-150818: Speed up logging.getLogger() for existing loggers (GH-150825)#150825
vsajip merged 2 commits into
python:mainfrom
gaborbernat:opt/logging-getlogger-fastpath

gaborbernat commented Jun 2, 2026 •
edited by bedevere-app Bot
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