Steven Phillips created DRILL-4081:
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Summary: Handle schema changes in ExternalSort
Key: DRILL-4081
URL: https://issues.apache.org/jira/browse/DRILL-4081
Project: Apache Drill
Issue Type: Improvement
Reporter: Steven Phillips
Assignee: Steven Phillips
This improvement will make use of the Union vector to handle schema changes.
When a new schema appears, the schema will be "merged" with the previous
schema. The result will be a new schema that uses Union type to store the
columns where this is a type conflict. All of the batches (including the
batches that have already arrived) will be coerced into this new schema.
A new comparison function will be included to handle the comparison of Union
type. Comparison of union type will work as follows:
1. All numeric types can be mutually compared, and will be compared using Drill
implicit cast rules.
2. All other types will not be compared against other types, but only among
values of the same type.
3. There will be an overall precedence of types with regards to ordering. This
precedence is not yet defined, but will be as part of the work on this issue.
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