[core] Reject unsafe MULTISET element evolution at DDL time - #10291
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A multiset element is physically a map key. A map key type cannot be cast on read (see SchemaEvolutionUtil#createMapCastExecutor), and a MULTISET-to-MULTISET cast cannot be resolved at all, so evolving a multiset element (type or nullability) is not read-safe. NestedSchemaUtils used to descend into the element and generate the change, which then either failed with a misleading ColumnNotExistException (master) or silently broke reads of existing data files. Reject any multiset element change in handleMultisetTypeUpdate with a clear message instead.
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Purpose
Altering the element type (or element nullability) of a
MULTISETcolumn threw a misleadingColumnNotExistException: the nested type-update walk inNestedSchemaUtilshad noMULTISETcase, so an off-by-one routed the change toupdateLastColumnon an empty list. AMULTISET<T>is physically stored asInternalMap<T, Int>, so the element is a map key, and the read-side cast infrastructure (SchemaEvolutionUtil) has no MULTISET executor andcreateMapCastExecutordeliberately forbids changing a map key type. So a multiset element type change cannot be applied to existing data.This rejects a multiset element modification at DDL time with a clear, actionable message ("Cannot update the element type of MULTISET column ... a multiset element is a map key, whose type cannot be evolved") instead of the misleading
ColumnNotExistException. TheMULTISETcolumn's own top-level nullability change (the column, not its element) is unaffected and keeps working.This closes #10290.
Tests
NestedSchemaUtilsTestasserts that changing a multiset element type, element nullability, or a complex multiset element is rejected with the clear message (testMultisetElementTypeChangeRejected,...NullabilityChangeRejected,...OfComplexTypeRejected).testMultisetTypeUpdateNullabilitypins that the multiset column's own nullability change still applies.API and Format
No.
Documentation
No.