[Python] Expand SDF by default in PortableRunner by Eliaaazzz · Pull Request #37965 · apache/beam

Eliaaazzz · 2026-03-26T14:01:40Z

Python iobase.Read uses a Splittable DoFn internally. PortableRunner's default batch pre-optimization path did not include translations.expand_sdf, so portable runners that do not support SDFs natively can receive a single SDF ParDo for reads. In Spark, that means Python reads such as ReadFromParquet may execute on a single partition without parallelization.

This change:

adds translations.expand_sdf to PortableRunner's default optimization phases
allows --experiments=pre_optimize=expand_sdf as an explicit custom phase
adds optimizer coverage for:
- default SDF expansion
- explicit pre_optimize=expand_sdf
- beam.io.Read(BoundedSource) expansion, including the expected RESHUFFLE

The bounded read test covers the issue scenario behind ReadFromParquet and similar Python Read transforms by verifying that the optimized pipeline contains the SDF component stages:

PAIR_WITH_RESTRICTION
SPLIT_AND_SIZE_RESTRICTIONS
PROCESS_SIZED_ELEMENTS_AND_RESTRICTIONS
RESHUFFLE

Local verification:

git diff --check
python -m compileall sdks/python/apache_beam/runners/portability/portable_runner.py sdks/python/apache_beam/runners/portability/portable_runner_test.py

Enable translations.expand_sdf in PortableRunner's default pre-optimization path so Python Read transforms are expanded for portable runners like Spark. Also add optimizer coverage for default SDF expansion, explicit pre_optimize=expand_sdf, and bounded Read expansion.\n\nRefs apache#24422.

gemini-code-assist · 2026-03-26T14:02:07Z

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request resolves a critical issue in Apache Beam's PortableRunner where Python iobase.Read operations, which internally utilize Splittable DoFns (SDFs), were not being properly parallelized on certain portable runners like Spark. The fix involves integrating the translations.expand_sdf optimization phase into the PortableRunner's default pipeline optimization process. This ensures that SDFs are correctly expanded into their constituent stages, thereby enabling parallel execution for read transforms and preventing performance bottlenecks, particularly for operations like ReadFromParquet.

Highlights

Default SDF Expansion: The expand_sdf optimization phase was added to the PortableRunner's default pre-optimization path to ensure proper parallelization of iobase.Read operations.
Explicit SDF Expansion: Users can now explicitly enable SDF expansion using the --experiments=pre_optimize=expand_sdf flag.
Enhanced Test Coverage: New tests were introduced to verify the correct expansion of SDFs in both default and explicit optimization scenarios, including beam.io.Read(BoundedSource) with expected RESHUFFLE for parallelization.

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github-actions · 2026-03-26T15:34:22Z

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R: @damccorm for label python.

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github-actions · 2026-04-03T12:27:17Z

Reminder, please take a look at this pr: @damccorm

damccorm · 2026-04-03T14:12:34Z

I'm not sure we can do this safely without potentially impacting performance of portable runners which do implement SDF; so I'm a bit worried about taking this

Abacn · 2026-04-03T15:23:32Z

Thanks for sharing the finding. Would you mind triggering the following PostCommit:

Make any change to

github/trigger_files/beam_PostCommit_Python_ValidatesRunner_Flink.json
.github/trigger_files/beam_PostCommit_Python_ValidatesRunner_Spark.json
.github/trigger_files/beam_PostCommit_XVR_Spark3.json
.github/trigger_files/beam_PostCommit_XVR_Flink.json

and push the commit

Abacn · 2026-04-03T15:25:43Z

@@ -332,7 +336,7 @@ def _optimize_pipeline(
        phases = []
        for phase_name in pre_optimize.split(','):
          # For now, these are all we allow.
-          if phase_name in ('pack_combiners', 'lift_combiners'):
+          if phase_name in ('pack_combiners', 'lift_combiners', 'expand_sdf'):


If there are compatibility/performance worries, this one is safer (opt in)

Eliaaazzz · 2026-04-04T03:32:57Z

I'm not sure we can do this safely without potentially impacting performance of portable runners which do implement SDF; so I'm a bit worried about taking this

Thanks， that makes sense. I agree that enabling this in the default pre-optimization path is too broad if it may impact runners that already support SDF well.

I’ll scope this down to the opt-in path only by dropping the default expand_sdf change and keeping only explicit pre_optimize=expand_sdf support together with the related tests.

Eliaaazzz · 2026-04-04T03:34:37Z

Thanks for sharing the finding. Would you mind triggering the following PostCommit:

Make any change to

github/trigger_files/beam_PostCommit_Python_ValidatesRunner_Flink.json

.github/trigger_files/beam_PostCommit_Python_ValidatesRunner_Spark.json

.github/trigger_files/beam_PostCommit_XVR_Spark3.json

.github/trigger_files/beam_PostCommit_XVR_Flink.json

and push the commit

Thanks, happy to do that.

I’ll make a no-op change to those trigger files to kick off the requested PostCommits and push the commit.

Eliaaazzz · 2026-04-04T09:01:45Z

All postCommit tests passed.

Abacn

Thanks!

Abacn · 2026-04-08T21:26:08Z

test_async_computation_result_cancel (apache_beam.runners.interactive.interactive_beam_test.InteractiveBeamComputeTest) failed

>     for p in self._pid_to_pipelines.values():
E     RuntimeError: dictionary changed size during iteration

test failure not related to the change. Wait until PreCommit YAML Xlang Direct becomes green on HEAD to merge

Eliaaazzz · 2026-04-09T10:11:50Z

test_async_computation_result_cancel (apache_beam.runners.interactive.interactive_beam_test.InteractiveBeamComputeTest) failed

>     for p in self._pid_to_pipelines.values():
E     RuntimeError: dictionary changed size during iteration
test failure not related to the change. Wait until PreCommit YAML Xlang Direct becomes green on HEAD to merge

Thanks a lot for taking the time to review this, I really appreciate it!

github-actions · 2026-04-16T12:38:16Z

Reminder, please take a look at this pr: @damccorm

damccorm · 2026-04-16T13:44:09Z

test_async_computation_result_cancel (apache_beam.runners.interactive.interactive_beam_test.InteractiveBeamComputeTest) failed

>     for p in self._pid_to_pipelines.values():
E     RuntimeError: dictionary changed size during iteration
test failure not related to the change. Wait until PreCommit YAML Xlang Direct becomes green on HEAD to merge

This has happened - @Eliaaazzz would you mind pulling in the latest changes from the master branch and committing to retrigger the test suite?

…g/issue-24422-expand-sdf-default-portable-runner

Eliaaazzz · 2026-04-17T14:57:35Z

test_async_computation_result_cancel (apache_beam.runners.interactive.interactive_beam_test.InteractiveBeamComputeTest) failed

>     for p in self._pid_to_pipelines.values():
E     RuntimeError: dictionary changed size during iteration
test failure not related to the change. Wait until PreCommit YAML Xlang Direct becomes green on HEAD to merge
This has happened - @Eliaaazzz would you mind pulling in the latest changes from the master branch and committing to retrigger the test suite?

Thanks, Done. I have pulled in the latest from master and pushed to retrigger CI.

codecov · 2026-04-17T15:26:12Z

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 56.74%. Comparing base (5a65f6e) to head (6fac01e).
⚠️ Report is 186 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master   #37965      +/-   ##
============================================
- Coverage     56.85%   56.74%   -0.11%     
  Complexity     3424     3424              
============================================
  Files          1178     1182       +4     
  Lines        187910   188752     +842     
  Branches       3586     3586              
============================================
+ Hits         106828   107111     +283     
- Misses        77694    78253     +559     
  Partials       3388     3388

Flag	Coverage Δ
python	`79.59% <100.00%> (-0.50%)`	⬇️

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Abacn · 2026-04-17T17:32:26Z

there is a known GHA issue that slowest matrix workflows get cancelled randomly. Otherwise all tests passed, thanks!

Eliaaazzz · 2026-04-18T01:43:42Z

there is a known GHA issue that slowest matrix workflows get cancelled randomly. Otherwise all tests passed, thanks!

Thank you for letting me know that, appreciate it!

github-actions Bot added python runners labels Mar 26, 2026

Eliaaazzz force-pushed the users/qingfengrumeng/issue-24422-expand-sdf-default-portable-runner branch from 60a831e to 169645d Compare March 26, 2026 14:26

github-actions Bot added the Next Action: Reviewers label Mar 26, 2026

Eliaaazzz force-pushed the users/qingfengrumeng/issue-24422-expand-sdf-default-portable-runner branch 4 times, most recently from e54f3d3 to 2641d1f Compare March 27, 2026 12:25

[python] Fix formatting for PortableRunner SDF optimization

2641d1f

github-actions Bot added the slow-review label Apr 3, 2026

github-actions Bot removed the slow-review label Apr 3, 2026

Abacn reviewed Apr 3, 2026

View reviewed changes

Make expand_sdf portable pre_optimize opt-in

f86b073

Abacn approved these changes Apr 8, 2026

View reviewed changes

github-actions Bot added the slow-review label Apr 16, 2026

github-actions Bot removed the slow-review label Apr 16, 2026

Merge remote-tracking branch 'origin/master' into users/qingfengrumen…

02d6035

…g/issue-24422-expand-sdf-default-portable-runner

chore: retrigger CI

6fac01e

Abacn approved these changes Apr 17, 2026

View reviewed changes

damccorm merged commit 79fb360 into apache:master Apr 20, 2026
133 of 137 checks passed

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