[BigQueryIO] Support reading from empty tables using Storage Read API in streaming pipelines

[stankiewicz]

This PR fixes an issue where BigQueryIO.read().withMethod(Method.DIRECT_READ) fails with an UnsupportedOperationException when reading from an empty table in a streaming pipeline.

In streaming pipelines, a BoundedSource (like BigQuery Storage Read) is wrapped in UnboundedReadFromBoundedSource. When the Storage Read API returns no streams (e.g., for an empty table or when all rows are pruned), the split() method returns an empty list.

The UnboundedReadFromBoundedSource adapter handles an empty split list by falling back to the original source and calling its createReader() method. Previously, BigQueryStorageSourceBase always threw UnsupportedOperationException in createReader(), assuming it must always be split first.

Changes

• Updated BigQueryStorageSourceBase.createReader() to return a new EmptyReader if split() confirms there are no streams to read.
• Added a private EmptyReader implementation that gracefully handles the absence of data.
• Preserved the UnsupportedOperationException fallback for cases where split() fails or returns data, ensuring backward compatibility with existing tests and runner expectations for non-empty sources.
• Added testUnboundedReadFromBoundedSourceWithEmptyTable to BigQueryIOStorageReadTest to specifically reproduce and verify this scenario.

Fixes #38007

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[gemini-code-assist]

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 a runtime exception that occurs when using the BigQuery Storage Read API in streaming pipelines with empty tables. By introducing a specialized reader for empty sources, the system can now correctly handle scenarios where no data streams are returned, ensuring robust behavior without breaking existing functionality for non-empty sources.

Highlights

• Empty Table Handling: Updated BigQueryStorageSourceBase.createReader() to return an EmptyReader when split() indicates no data is available, preventing an UnsupportedOperationException.
• EmptyReader Implementation: Introduced a private EmptyReader class to gracefully handle reading from empty BigQuery tables in streaming pipelines.
• Regression Testing: Added testUnboundedReadFromBoundedSourceWithEmptyTable to verify that empty tables no longer cause pipeline failures.

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[stankiewicz]

/gemini review

[gemini-code-assist]

Code Review

This pull request modifies BigQueryStorageSourceBase to handle empty data sources by returning an EmptyReader instead of throwing an UnsupportedOperationException. This is determined by attempting a split and checking if the result is empty. A new test case in BigQueryIOStorageReadTest verifies this behavior. The review feedback recommends adding debug logging when catching exceptions during the split check to prevent silent failures of underlying issues like authentication or quota errors.

[stankiewicz]

Run Java_GCP_IO_Direct PreCommit

[stankiewicz]

flakes around not related:

> Task :sdks:java:io:google-cloud-platform:integrationTest
StorageApiSinkSchemaUpdateIT > testExactlyOnceWithAutoSchemaUpdate[0] FAILED
    com.google.api.client.googleapis.json.GoogleJsonResponseException at StorageApiSinkSchemaUpdateIT.java:554
StorageApiSinkSchemaUpdateIT > testAtLeastOnceWithIgnoreUnknownValues[1] FAILED
    java.lang.RuntimeException at StorageApiSinkSchemaUpdateIT.java:554
        Caused by: com.google.api.client.googleapis.json.GoogleJsonResponseException at StorageApiSinkSchemaUpdateIT.java:554
StorageApiSinkSchemaUpdateIT > testAtLeastOnceDynamicDestinationsWithAutoSchemaUpdate[2] FAILED
    java.lang.RuntimeException at StorageApiSinkSchemaUpdateIT.java:530
        Caused by: com.google.api.client.googleapis.json.GoogleJsonResponseException at StorageApiSinkSchemaUpdateIT.java:530

[stankiewicz]

assign set of reviewers

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[Abacn]

Thank you!