Fix BigQuery Storage Write API stream count for batch writes

[SPUERSAIYAN]

What changed

Fixes #38770

This fixes handling of num_storage_api_streams / num_streams for BigQuery Storage Write API batch writes.

Previously, the Java schema transform only applied num_streams inside the unbounded pipeline branch, so bounded batch pipelines using the Storage Write API ignored the configured fixed stream count. This change applies withNumStorageWriteApiStreams(...) whenever num_streams > 0, while keeping triggering frequency and auto-sharding behavior limited to unbounded pipelines.

Details

• Applies fixed Storage Write API stream counts to bounded and unbounded schema transform writes.
• Keeps auto_sharding as an unbounded-only option.
• Removes outdated documentation that described num_storage_api_streams / num_streams as streaming-only.
• Updates Java, Python, and website docs to reflect batch support.
• Adds a bounded pipeline translation test that verifies fixed stream counts produce the expected batch redistribute step.

Validation

• git diff --check
• ./gradlew.bat --no-daemon --console=plain :sdks:java:io:google-cloud-platform:spotlessCheck

CHANGES.md

Not updated because this is a targeted behavior/documentation fix rather than a broad user-facing feature addition.

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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 addresses an issue where batch pipelines using the BigQuery Storage Write API were unable to utilize fixed stream counts. By modifying the schema transform logic, the changes ensure that configured stream counts are respected in batch contexts, while maintaining existing auto-sharding behavior exclusively for streaming pipelines. The update also cleans up documentation and includes a validation test to ensure consistent behavior across pipeline types.

Highlights

• BigQuery Storage Write API Support: Enabled the use of fixed stream counts for batch pipelines using the BigQuery Storage Write API, allowing for better control over parallelism.
• Logic Refinement: Restricted auto-sharding behavior to unbounded pipelines while ensuring fixed stream counts are correctly applied to both bounded and unbounded writes.
• Documentation Updates: Updated Java, Python, and website documentation to clarify that fixed stream counts are supported for both batch and streaming pipelines.
• Testing: Added a new bounded pipeline translation test to verify that fixed stream counts correctly trigger the expected redistribute step.

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Code Review

This pull request updates the BigQuery Storage Write API implementation and documentation to support configuring the number of write streams for both batch and streaming pipelines, rather than limiting it to streaming pipelines. It modifies the schema transform provider to apply the stream count configuration to both bounded and unbounded writes and adds a corresponding unit test. The review feedback highlights two issues in the schema transform provider: a lack of validation for negative stream counts and an issue where explicitly setting the stream count to zero is ignored, preventing users from overriding pipeline options. A code suggestion is provided to resolve these issues.

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[stankiewicz]

I see there is also #38776 , which looks a bit simpler.

[SPUERSAIYAN]

我看到还有#38776，看起来比较简单一些。

Thanks for pointing this out. I understand that #38776 is another PR with a smaller change to this issue.

If #38776 already fixes the problem, I’m happy to close this PR to avoid duplicate work