Paul Rogers created DRILL-6046:
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Summary: Define semantics of vector metadata
Key: DRILL-6046
URL: https://issues.apache.org/jira/browse/DRILL-6046
Project: Apache Drill
Issue Type: Improvement
Affects Versions: 1.10.0
Reporter: Paul Rogers
Priority: Minor
Vectors provide metadata in the form of the {{MaterializedField}}. This class
has evolved in an ad-hoc fashion over time, resulting in inconsistent behavior
across vectors. The inconsistent behavior causes bugs and slow development
because each vector follows different rules. Consistent behavior would, by
contrast, lead to faster development and fewer bugs by reducing the number of
variations that code must handle.
Issues include:
* Map vectors, but not lists, can create contents given a list of children in
the {{MaterializedField}} passed to the constructor.
* {{MaterializedField}} appears to want to be immutable, but it does allow
changing of children. Unions also want to change the list of subtypes, but that
is in the immutable {{MajorType}}, causing unions to rebuild and replace its
{{MaterializedField}} on addition of a new type. By contrast, maps do not
replace the field, they just add children.
* Container vectors (maps, unions, lists) hold references to child
{{MaterializedFields}}. But, because unions replace their fields, parents
become out of sync since they point to the old, version before the update,
causing inconsistent metadata, so that code cannot trust the metadata.
* Lists and maps, but not unions, list their children in the field.
* Nullable types, but not repeated types, include internal vectors in their
list of children.
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