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This FLIP does not discuss runtime handling of the primary key information by sources and sinks. This additional information will not change the way how upsert sources and sinks work (We do not support UPSERT sources yet. For sinks we will stick to the current validation implementation). Usage of the primary key for upsert sources and sinks shall be discussed in a separate FLIP. This will not alter any UpsertSink implementations. This is merely a metadata information for optimization. We might use it in the future for query validation, e.g. validate that we perform upserts on the whole key, or use autogenerated values for missing fields etc.

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