[Bug]: [Python] DirectRunner Prism fallback to BundleBasedDirectRunner fails with NotImplementedError on batched DoFns (WriteToParquet)

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难度
4/5
预计耗时
3-5 天
新手友好度
48/100
Issue 类型
缺陷
描述清晰度
基本清楚
活跃度
活跃
技术栈
python
领域
backend, data-engineering

调研方向

Start in sdks/python/apache_beam/runners/direct/direct_runner.py, especially the SwitchingDirectRunner fallback around lines 141–146 and 204–230; compare its behavior with FnApiRunner for process_batch transforms. Reproduce with the provided WriteToParquet pipeline, then check relevant direct runner tests. Done means the fallback runs batched DoFns successfully without breaking the existing runner paths.

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描述

awaiting triage bug P2 python
What happened?

When running a Python or Beam YAML pipeline with the default DirectRunner (SwitchingDirectRunner), if PrismRunner is bypassed (for example when the pipeline contains an external cross-language transform per direct_runner.py:141) or cannot start (offline environment / restricted container where the Prism binary cannot be downloaded or executed), SwitchingDirectRunner falls back to BundleBasedDirectRunner.

If the pipeline includes WriteToParquet (or any transform using DoFn.process_batch), execution then fails with NotImplementedError, even though the in-process FnApiRunner executes the exact same pipeline cleanly.

Minimal reproducer (forcing the non-Prism fallback path):

import tempfile, apache_beam as beam, pyarrow as pa

schema = pa.schema([('id', pa.int64()), ('name', pa.string())])
with tempfile.TemporaryDirectory() as d:
  with beam.Pipeline(runner='BundleBasedDirectRunner') as p:
    (p
     | beam.Create([{'id': 1, 'name': 'Ada'}])
     | beam.io.WriteToParquet(f'{d}/out', schema=schema))

Cause

In sdks/python/apache_beam/runners/direct/direct_runner.py (lines 141–146 and 204–230), SwitchingDirectRunner unconditionally falls back to BundleBasedDirectRunner(), which does not implement process_batch for batched PyArrow DoFns (FnApiRunner does). Checking for process_batch transforms (or routing batch pipelines without TestStream/unbounded state to FnApiRunner when Prism is unavailable) avoids the failure.

Issue Priority

Priority: 2 (default / most bugs should be filed as P2)

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