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https://issues.apache.org/jira/browse/DRILL-6435?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16488268#comment-16488268
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ASF GitHub Bot commented on DRILL-6435:
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paul-rogers commented on issue #1286: DRILL-6435: MappingSet is stateful, so it
can't be shared between threads
URL: https://github.com/apache/drill/pull/1286#issuecomment-391554391
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; but I wonder what
other things will be broken since the original design appeared to be that
`MappingSet`s are static.
At the very least, perhaps we'd want to add a comment explaining why we need
per-query modifications rather than the standard, static definitions.
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> 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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