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https://issues.apache.org/jira/browse/DRILL-6373?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16551787#comment-16551787
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ASF GitHub Bot commented on DRILL-6373:
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vrozov commented on issue #1244: DRILL-6373: Refactor Result Set Loader for
Union, List support
URL: https://github.com/apache/drill/pull/1244#issuecomment-406811356
@paul-rogers The change to `NullableVarCharVector` that was part of your PR
exposed a bug that is part of the existing code. Please see
`AbstractMapVector.java:48`. The problem is that a newly created map vector
references a newly created deep copy(clone) of the passed `MaterializedField`
while newly created child vectors of the map vector references children of
**another** instance of the `MaterializeField`. If that **other** instance is
completely immutable it would not cause any problem (except that now there is
no reason to create deep copy), but with your changes there was an attempt to
mutate from different threads the **other** instance as that **other** instance
is used to create multiple outgoing vectors. I hope that this explains what I
mean when referring to **existing** bug.
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> Refactor the Result Set Loader to prepare for Union, List support
> -----------------------------------------------------------------
>
> Key: DRILL-6373
> URL: https://issues.apache.org/jira/browse/DRILL-6373
> Project: Apache Drill
> Issue Type: Improvement
> Affects Versions: 1.13.0
> Reporter: Paul Rogers
> Assignee: Paul Rogers
> Priority: Major
> Attachments: 6373_Functional_Fail_07_13_1300.txt,
> drill-6373-with-6585-fix-functional-failure.txt
>
>
> As the next step in merging the "batch sizing" enhancements, refactor the
> {{ResultSetLoader}} and related classes to prepare for Union and List
> support. This fix follows the refactoring of the column accessors for the
> same purpose. Actual Union and List support is to follow in a separate PR.
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