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Spec: Clarify that readers must accept promotable types in any data file - #18404
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…a files Readers should accept data file columns whose type is promotable to the field's current type, not just an exact match. This handles the case where a file was written before a type promotion occurred.
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October 7, 2026 01:10
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Type promotion lets a field evolve, for example from DECIMAL(8. 0) to DECIMAL(25. 0)without rewriting data files. Existing Parquet files keep storing the column as int32 with DECIMAL(8. 0) and readers must read them as DECIMAL(25, 0).
The spec addresses reading narrower types in the context of schema evolution. However, schema evolution can potentially leave no markers in the metadata and so readers must be prepared to read narrower types than the type specified in the schema.
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