stankiewicz opened a new pull request, #38009:
URL: https://github.com/apache/beam/pull/38009
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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