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https://issues.apache.org/jira/browse/DRILL-6435?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16488264#comment-16488264
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Paul Rogers commented on DRILL-6435:
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The specific fix may be OK, but I believe it overlooks a broader point. The
{{MappingSet}} is supposed to be a static association of elements used in code
generation. This mapping is meant to be static and thus sharable.
If there is an issue, then somewhere we must have added code that alters these
objects per-query. We might want to back up and find that use, then ask if it
is really necessary.
If so, then making the objects non-static makes sense. Perhaps we'd want to add
a comment explaining why we need per-query modifications rather than the
standard, static definitions.
> MappingSet is stateful, so it can't be shared between threads
> -------------------------------------------------------------
>
> Key: DRILL-6435
> URL: https://issues.apache.org/jira/browse/DRILL-6435
> Project: Apache Drill
> Issue Type: Bug
> Reporter: Vlad Rozov
> Assignee: Vlad Rozov
> Priority: Major
>
> There are several instances where static {{MappingSet}} instances are used
> (for example {{NestedLoopJoinBatch}} and {{BaseSortWrapper}}). This causes
> instance reuse across threads when queries are executed concurrently. As
> {{MappingSet}} is a stateful class with visitor design pattern, such reuse
> causes invalid state.
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