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https://issues.apache.org/jira/browse/HIVE-12508?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15026599#comment-15026599
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Jesus Camacho Rodriguez commented on HIVE-12508:
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I am not completely sure of my sentence above:
{quote}...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.{quote}
I need to understand better the issue on the Calcite side. I think this rule,
even when run in isolation, could create cycles depending on the plan, and
these cycles could lead to the problem retrieving the metadata.
> 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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