valuekind

[ahmedabu98]

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Summary of Changes

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This pull request introduces support for Change Data Capture (CDC) metadata by adding a ValueKind concept throughout the Apache Beam SDK and Fn API. This allows for explicit tracking of data changes (INSERT, UPDATE, DELETE) in windowed elements, ensuring this metadata is correctly propagated through the execution pipeline, including serialization in Windmill and accessibility within user-defined DoFn logic.

Highlights

• ValueKind Introduction: Introduced a new ValueKind enum to represent CDC metadata (INSERT, UPDATE_BEFORE, UPDATE_AFTER, DELETE) and integrated it into the Beam Fn API and core SDK.
• API Expansion: Added outputWithKind methods to DoFn.WindowedContext and related runners to allow users to specify the ValueKind during output operations.
• Dataflow Integration: Updated WindmillSink and UngroupedWindmillReader to correctly encode and decode ValueKind metadata in Windmill messages.
• Reflect and Invoker Updates: Updated DoFnInvoker and ByteBuddyDoFnInvokerFactory to support ValueKind as a parameter in DoFn methods.

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