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https://issues.apache.org/jira/browse/HIVE-12508?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15025601#comment-15025601
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Jesus Camacho Rodriguez commented on HIVE-12508:
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The issue was (if I recall well) that you end up with cycles in the planning
graph (between equivalent sets of expressions) and then a metadata provider can
fire up indefinitely.
But I guess that as currently we execute this rule in isolation in Hive, and we
know this rule will not produce cycles, we could close it as the metadata
provider will never fire up indefinitely.
> HiveAggregateJoinTransposeRule places a heavy load on the metadata system
> -------------------------------------------------------------------------
>
> Key: HIVE-12508
> URL: https://issues.apache.org/jira/browse/HIVE-12508
> Project: Hive
> Issue Type: Bug
> Components: CBO
> Affects Versions: 2.0.0
> Reporter: Jesus Camacho Rodriguez
> Assignee: Jesus Camacho Rodriguez
> Attachments: HIVE-12508.patch
>
>
> Finding out whether the input is already unique requires a call to
> areColumnsUnique that currently (until CALCITE-794 is fixed) places a heavy
> load on the metadata system. This can lead to long CBO planning.
> This is a temporary fix that avoid the call to the method till then.
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