[jira] [Updated] (DRILL-4081) Handle schema changes in ExternalSort

["Suresh Ollala (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/DRILL-4081?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Suresh Ollala updated DRILL-4081:
---------------------------------
    Reviewer: Victoria Markman

> 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
>             Fix For: 1.4.0
>
>
> 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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