difin opened a new pull request, #6927:
URL: https://github.com/apache/hive/pull/6927
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### What changes were proposed in this pull request?
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Fixes for the Iceberg format-v3 `UNKNOWN` type support. Before this change,
`INSERT INTO t (col list) ...` failed on Iceberg tables that have `UNKNOWN`
columns, and several other read, write and DDL paths did not handle the type.
`UNKNOWN` columns are always NULL and are never written to data files; this PR
makes Hive follow those rules end to end.
**Serde / type system (`serde`)**
- `TypeInfoUtils`: implicit conversion of a NULL literal to `UNKNOWN` now
also works inside structs (e.g. `named_struct('x', 5, 'u', NULL)` into
`STRUCT<x:INT, u:UNKNOWN>`), which is what column-list inserts and `INSERT ...
SELECT` need.
- `ObjectInspectorUtils` / `SerDeUtils`: added the missing `UNKNOWN` cases
(copy, compare, hash, string conversion, constant object inspectors).
- New `UnknownConstantObjectInspector` for NULL constants typed as
`UNKNOWN`. Non-NULL values are rejected with "UNKNOWN type columns only accept
NULL values".
**Query layer (`ql`)**
- `VectorUDFStructField`: extracting an `UNKNOWN` struct field in vectorized
mode returns a repeating NULL vector.
- `Table`: views can expose `UNKNOWN` columns (e.g. `CREATE VIEW AS SELECT`
over an Iceberg table). Non-Iceberg tables still reject the type.
- `DDLPlanUtils`: `SHOW CREATE TABLE` prints `UNKNOWN` columns instead of
failing with "Unknown type: UNKNOWN".
**Iceberg handler**
- DDL validation (`BaseHiveIcebergMetaHook`, `IcebergTableUtil`,
`HiveSchemaUtil`). UNKNOWN values have no physical representation in data
files, so the following are rejected with clear errors:
- `UNKNOWN` as an array element type, or as a map key or value type;
- structs whose fields are all `UNKNOWN`;
- partitioning by an `UNKNOWN` column, both in `PARTITIONED BY` and in
`ALTER TABLE ... SET PARTITION SPEC`;
- non-NULL defaults (`DEFAULT NULL` is allowed);
- `UNKNOWN` on format-version 2 tables (Iceberg's own check).
- Type promotion (`HiveIcebergMetaHook`): the v3 spec allows `ALTER TABLE
... CHANGE COLUMN` to promote `UNKNOWN` to any primitive type, but Iceberg 1.x
does not implement it yet
([apache/iceberg#18305](https://github.com/apache/iceberg/issues/18305)). Until
it does, Hive commits the new schema directly through `TableOperations`,
retrying on commit conflicts. The field ID is kept, so existing files read the
column as NULL and the metadata matches what a native promotion would produce.
Rename, comment and reorder in the same statement still go through
`UpdateSchema`. This workaround can be replaced by `UpdateSchema.updateColumn`
once Iceberg supports the promotion.
- Vectorized ORC reads (`VectorizedReadUtils`): Iceberg's ORC projection
drops `UNKNOWN` fields, but Hive's vectorized reader matches columns by
position, so later columns were misaligned (AIOOBE / ClassCastException). The
read schema now keeps a placeholder column for each `UNKNOWN` field, which ORC
returns as NULL.
**Tests**
- `TestHiveIcebergUnknownType`: read/write, DDL, column-list insert with
UPDATE and DELETE, promotion (field ID kept, time travel to before promotion),
rejection cases, `SHOW CREATE TABLE`, `REPLACE COLUMNS`. Runs on Parquet, ORC
and Avro, vectorized and non-vectorized.
- q-tests: `positive/unknown_type.q` covers DML, MERGE, CTAS/CTLT, views,
joins, aggregates, window functions, ANALYZE, promotion, tags, ORC, Avro and
`SHOW CREATE TABLE`. Eleven `negative/unknown_type_*.q` files cover each
rejection.
`VARIANT` is out of scope for this PR.
### Why are the changes needed?
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### Does this PR introduce _any_ user-facing change?
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