Liya Fan created ARROW-6420:
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Summary: [Java] Improve the performance of UnionVector when
getting underlying vectors
Key: ARROW-6420
URL: https://issues.apache.org/jira/browse/ARROW-6420
Project: Apache Arrow
Issue Type: Improvement
Components: Java
Reporter: Liya Fan
Assignee: Liya Fan
Getting the underlying vector is a frequent opertation for UnionVector. It
relies on this operation to get/set data at each index.
The current implementation is inefficient. In particular, it first gets the
minor type at the given index, and then compares it against all possible minor
types in a switch statment, until a match is found.
We improve the performance by storing the internal vectors in an array, whose
index is the ordinal of the minor type. So given a minor type, its
corresponding underlying vector can be obtained in O(1) time.
It should be noted that this technique is also applicable to UnionReader and
UnionWriter, and support for UnionReader is already implemented.
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