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https://issues.apache.org/jira/browse/DRILL-4081?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15006124#comment-15006124
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ASF GitHub Bot commented on DRILL-4081:
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GitHub user StevenMPhillips opened a pull request:
https://github.com/apache/drill/pull/257
DRILL-4081: Handle schema changes in ExternalSort
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/StevenMPhillips/drill drill-4081
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/drill/pull/257.patch
To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:
This closes #257
----
commit db573ffe2c15caad4a9d12dab9d28cc3e0b2f51d
Author: Steven Phillips <[email protected]>
Date: 2015-11-13T19:27:16Z
DRILL-4081: Handle schema changes in ExternalSort
----
> 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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