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NoahStapp · 2026-02-26T21:24:50Z

Changes in this PR

Add four optimizations to the C extension BSON implementation:

Skip _type_marker lookup for common built-in types.
Use PyDict_New() instead of PyObject_CallObject() where possible.
Use PyDict_SetItem() instead of PyObject_SetItem() where possible.
Use PyObject_Vectorcall() and its ilk instead of PyObject_CallFunctionObjArgs() and similar functions.

These changes result in the following BSON benchmark performance improvements on Python 3.14.3:

# Before
Completed TestFlatEncoding 462.762 MB/s, MEDIAN=0.131s, total time=30.105s, iterations=230
Completed TestFlatDecoding 437.150 MB/s, MEDIAN=0.138s, total time=30.060s, iterations=217
Completed TestDeepEncoding 165.417 MB/s, MEDIAN=0.119s, total time=30.086s, iterations=252
Completed TestDeepDecoding 158.894 MB/s, MEDIAN=0.124s, total time=30.116s, iterations=242
Completed TestFullEncoding 274.749 MB/s, MEDIAN=0.147s, total time=30.073s, iterations=203
Completed TestFullDecoding 157.580 MB/s, MEDIAN=0.255s, total time=30.108s, iterations=116

# After
Completed TestFlatEncoding 547.545 MB/s, MEDIAN=0.110s, total time=30.074s, iterations=271
Completed TestFlatDecoding 446.351 MB/s, MEDIAN=0.135s, total time=30.041s, iterations=221
Completed TestDeepEncoding 206.715 MB/s, MEDIAN=0.095s, total time=30.084s, iterations=316
Completed TestDeepDecoding 177.857 MB/s, MEDIAN=0.111s, total time=30.081s, iterations=268
Completed TestFullEncoding 333.103 MB/s, MEDIAN=0.121s, total time=30.064s, iterations=247
Completed TestFullDecoding 165.150 MB/s, MEDIAN=0.244s, total time=30.032s, iterations=123

# Python 3.11.14, the last version before seeing significant regressions in Python internals
Completed TestFlatEncoding 559.832 MB/s, MEDIAN=0.011s, total time=0.108s, iterations=10
Completed TestFlatDecoding 475.089 MB/s, MEDIAN=0.013s, total time=0.103s, iterations=8
Completed TestDeepEncoding 209.326 MB/s, MEDIAN=0.009s, total time=0.104s, iterations=11
Completed TestDeepDecoding 167.511 MB/s, MEDIAN=0.012s, total time=0.106s, iterations=9
Completed TestFullEncoding 331.071 MB/s, MEDIAN=0.012s, total time=0.111s, iterations=9
Completed TestFullDecoding 173.523 MB/s, MEDIAN=0.023s, total time=0.117s, iterations=5

This represents up to a ~25% improvement for some benchmarks and brings them close to the high mark of Python 3.11 performance.

Test Plan

Verified with the existing test suite.

Checklist

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Pull request overview

This PR implements three performance optimizations to the BSON C extension to improve encode/decode performance by up to ~25% on Python 3.14, bringing it close to Python 3.11 performance levels.

Changes:

Skip expensive _type_marker attribute lookups for common built-in types that are known not to have this attribute
Use direct PyDict_New() API instead of generic PyObject_CallObject() when document_class is dict
Use direct PyDict_SetItem() API instead of generic PyObject_SetItem() when document_class is dict

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ShaneHarvey

Nice work!

ShaneHarvey

lgtm

codecov-commenter · 2026-02-27T02:19:02Z

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 87.57%. Comparing base (b60d266) to head (ec11ab8).
⚠️ Report is 5 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2715      +/-   ##
==========================================
+ Coverage   87.55%   87.57%   +0.01%     
==========================================
  Files         141      141              
  Lines       24098    24182      +84     
  Branches     4118     4146      +28     
==========================================
+ Hits        21100    21177      +77     
- Misses       2108     2114       +6     
- Partials      890      891       +1

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sleepyStick

lol this sent me straight to reading docs land so it took me a hot minute to review but i've learned!

PYTHON-5211 - Improve BSON encode/decode performance

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NoahStapp requested a review from Copilot February 26, 2026 21:24

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NoahStapp marked this pull request as ready for review February 26, 2026 21:40

NoahStapp requested a review from a team as a code owner February 26, 2026 21:40

NoahStapp requested review from ShaneHarvey and sleepyStick February 26, 2026 21:40

ShaneHarvey suggested changes Feb 26, 2026

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Comment thread bson/_cbsonmodule.c

Add Shane's suggestion

0c1b138

ShaneHarvey previously approved these changes Feb 26, 2026

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NoahStapp changed the title ~~PYTHON-5211 - Improve BSON encode/decode performance~~ PYTHON-5737 BSON encoding/decoding performance improvements Feb 26, 2026

NoahStapp changed the title ~~PYTHON-5737 BSON encoding/decoding performance improvements~~ PYTHON-5737 - BSON encoding/decoding performance improvements Feb 26, 2026

Use Vectorcall APIs

ec11ab8

NoahStapp dismissed ShaneHarvey’s stale review via ec11ab8 February 26, 2026 23:45

ShaneHarvey approved these changes Feb 27, 2026

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sleepyStick approved these changes Feb 27, 2026

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NoahStapp merged commit 469a32a into mongodb:master Mar 2, 2026
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File	Description
bson/_cbsonmodule.h	Add `is_dict_class` field to codec_options_t struct to track when document_class is dict
bson/_cbsonmodule.c	Implement three performance optimizations: skip _type_marker lookup for built-in types, use PyDict_New() and PyDict_SetItem() when possible

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PYTHON-5737 - BSON encoding/decoding performance improvements#2715

PYTHON-5737 - BSON encoding/decoding performance improvements#2715
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NoahStapp commented Feb 26, 2026 •

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