PYTHON-5977 APM/logging hot-path optimizations by NoahStapp · Pull Request #2968 · mongodb/mongo-python-driver

NoahStapp · 2026-07-30T19:13:14Z

Changes in this PR

The changes introduced by PYTHON-5903, PYTHON-5846, PYTHON-5745, and PYTHON-5676 caused small but measurable regressions for low-latency, high operation count workloads such as the DSI locust_ping benchmark. Much of this is due to constructing telemetry objects even when APM/logging is disabled and other similar changes that lie on the hot path for such workloads.

This PR attempts to optimize all of those regressions away and return performance to its point before their addition.

Test Plan

Standard test suite, benchmarks.

Results of a simple ping workload benchmark:

Metric	PR	main	main vs PR
Throughput	10,634/s	6,567/s	−38.8%
Mean latency	752 µs	1,219 µs	+62%
p50	~170 µs	~800 µs	~4–5× worse
p99	~5,000 µs	~7,000 µs	+40%

Checklist

Checklist for Author

~~[ ] Did you update the changelog (if necessary)?~~
~~[ ] Is there test coverage?~~
~~[ ] Is any followup work tracked in a JIRA ticket? If so, add link(s).~~

Checklist for Reviewer

Does the title of the PR reference a JIRA Ticket?
Do you fully understand the implementation? (Would you be comfortable explaining how this code works to someone else?)
Is all relevant documentation (README or docstring) updated?

codecov-commenter · 2026-07-30T19:46:37Z

Codecov Report

❌ Patch coverage is 98.40000% with 2 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
pymongo/_telemetry.py	90.47%	1 Missing and 1 partial ⚠️

📢 Thoughts on this report? Let us know!

NoahStapp · 2026-08-04T18:05:56Z

Failures are unrelated.

Copilot

Pull request overview

This PR targets performance regressions on low-latency, high-op-count workloads by removing avoidable APM/logging/telemetry work from hot paths when telemetry is disabled, while preserving existing behavior when telemetry is enabled.

Changes:

Gate operation-id generation and telemetry object construction behind “telemetry enabled” checks (APM listeners and/or DEBUG logging), especially on retry and bulk-write paths.
Reduce hot-path overhead in command execution, CMAP checkout/checkin, and server selection by skipping telemetry/logging work when disabled.
Add regression tests to ensure no RawBSON reply inflation and no operation-id generation when telemetry is disabled.

Reviewed changes

Copilot reviewed 19 out of 19 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
pymongo/_telemetry.py	Adds helper gating and streamlines command/CMAP/SDAM telemetry to avoid work when disabled.
pymongo/monitoring.py	Clarifies speculative-authentication redaction guard for potential RawBSONDocument inputs.
pymongo/message.py	Allows passing optional operation_id through bulk-write context types.
pymongo/asynchronous/command_runner.py	Skips command telemetry construction when APM/logging disabled; returns duration as seconds internally.
pymongo/synchronous/command_runner.py	Sync equivalent of the async command-runner hot-path gating and duration handling.
pymongo/asynchronous/mongo_client.py	Centralizes op-id generation gating for retries via _should_generate_op_id.
pymongo/synchronous/mongo_client.py	Sync equivalent of op-id generation gating for retries.
pymongo/asynchronous/bulk.py	Avoids op-id generation for bulk writes when telemetry disabled.
pymongo/synchronous/bulk.py	Sync equivalent bulk-write op-id gating.
pymongo/asynchronous/client_bulk.py	Avoids op-id generation for client bulk writes when telemetry disabled.
pymongo/synchronous/client_bulk.py	Sync equivalent client-bulk op-id gating and type adjustments.
pymongo/asynchronous/pool.py	Adds fast paths to skip CMAP telemetry/logging calls when disabled.
pymongo/synchronous/pool.py	Sync equivalent pool fast paths for CMAP telemetry/logging.
pymongo/asynchronous/topology.py	Avoids server-selection telemetry object creation and success logging when server-selection logging is disabled.
pymongo/synchronous/topology.py	Sync equivalent server-selection logging gating.
test/asynchronous/test_operation_id_retry.py	Adds coverage ensuring no op-id generation when telemetry disabled; covers bulk/client-bulk.
test/test_operation_id_retry.py	Sync generated equivalent test coverage for no-op-id behavior when telemetry disabled.
test/asynchronous/test_monitoring.py	Adds test ensuring CommandSucceededEvent redaction checks don’t inflate RawBSON replies for non-hello commands.
test/test_monitoring.py	Sync generated equivalent of the RawBSON inflation regression test.

Suppressed comments (1)

pymongo/_telemetry.py:108

Grammar: “fast path … inline this gate” should use the verb form “inlines” (and the following sentence should refer to a singular subject).

        # NOTE: the _run_command fast path in command_runner.py inline this gate for performance
        # They must be kept in sync with any gating changes

blink1073 · 2026-08-04T19:21:12Z

+    # Fast path: skip telemetry construction when logging and APM are disabled
+    # Inline enabled check here for performance
+    telemetry: Optional[_CommandTelemetry] = None
+    if (topology_id is not None and _COMMAND_LOGGER.isEnabledFor(logging.DEBUG)) or (


I think this part should be a helper in _telemetry.py

This is intentionally inlined here for performance since this is called on every single operation, moving to a helper is a small performance hit that compounds across each time the inlined check is abstracted.

blink1073 · 2026-08-04T19:23:13Z

            self.active_contexts.discard(conn.cancel_context)
-        self._telemetry.checked_in(conn.id)
+        telemetry = self._telemetry
+        if telemetry._should_publish or (


This logic should also be in _telemetry.py, perhaps as a property on the class

Same here as above, inlined intentionally for performance.

blink1073 · 2026-08-04T19:23:33Z

-        checkout_started_time = pool._telemetry.checkout_started()
+        telemetry = pool._telemetry
+        # Fast path: skip telemetry calls when CMAP events/logging are disabled
+        if not telemetry._should_publish and not (


Also could be factored into _telemetry.py

Same here as well.

blink1073 · 2026-08-04T19:24:07Z

-        ss.started()
+        # Server selection does not have APM events, gate only on logging
+        ss: Optional[_ServerSelectionTelemetry] = None
+        if _SERVER_SELECTION_LOGGER.isEnabledFor(logging.DEBUG):


Also can be factored into _telemetry.py

blink1073 · 2026-08-04T19:24:39Z

-            server.description.address[0],
-            server.description.address[1],
-        )
+        if _SERVER_SELECTION_LOGGER.isEnabledFor(logging.DEBUG):


Same here, we shouldn't need to have this type of logic in multiple places.

blink1073 · 2026-08-04T19:25:36Z

        }
-        op_id = _randint()
+        client = self.collection.database.client
+        op_id = _randint() if _should_generate_op_id(client._event_listeners) else None


Maybe this function should either return a _randint or None itself

NoahStapp added 3 commits July 28, 2026 11:27

APM-disabled optimizations

e46bac0

Use attempt -1 instead of attempt for backoff

a15d983

Final APM optimizations

2e67f48

NoahStapp added 6 commits July 30, 2026 16:21

Cleanup pass #1

5cbf327

Revert changes without significant performance bumps

f608c1a

Merge branch 'main' into BF-44986

5180580

Comment cleanup

6d58a7d

More clarity cleanup

345fd71

Remove unneeded properties

d61df7a

NoahStapp marked this pull request as ready for review August 4, 2026 18:05

NoahStapp requested a review from a team as a code owner August 4, 2026 18:05

NoahStapp requested review from aclark4life and Copilot August 4, 2026 18:05

Merge branch 'main' into BF-44986

788f19f

NoahStapp requested a review from blink1073 August 4, 2026 18:06

Copilot started reviewing on behalf of NoahStapp August 4, 2026 18:06 View session

Copilot AI reviewed Aug 4, 2026

View reviewed changes

Comment thread pymongo/_telemetry.py

blink1073 requested changes Aug 4, 2026

View reviewed changes

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PYTHON-5977 APM/logging hot-path optimizations - #2968

PYTHON-5977 APM/logging hot-path optimizations#2968
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