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https://issues.apache.org/jira/browse/HIVE-6873?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13965099#comment-13965099
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Remus Rusanu commented on HIVE-6873:
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[~jnp] From how I read GroupByOptimizer.java@227, I reckon there are some cases
when the reduce side does expect the mapper to had been doing the correct
aggregation:
{code}
// Partial aggregation is not done for distincts on the mapper
// However, if the data is bucketed/sorted on the distinct key,
partial aggregation
// can be performed on the mapper.
{code}
> DISTINCT clause in aggregates is handled incorrectly by vectorized execution
> ----------------------------------------------------------------------------
>
> Key: HIVE-6873
> URL: https://issues.apache.org/jira/browse/HIVE-6873
> Project: Hive
> Issue Type: Bug
> Components: Query Processor
> Affects Versions: 0.13.0, 0.14.0
> Reporter: Remus Rusanu
> Assignee: Remus Rusanu
> Attachments: HIVE-6873.1.patch, HIVE-6873.2.patch
>
>
> The vectorized aggregates ignore the DISTINCT clause. This cause incorrect
> results. Due to how GroupByOperatorDesc adds the DISTINCT keys to the overall
> aggregate keys the vectorized aggregates do account for the extra key, but
> they do not process the data correctly for the key. the reduce side the
> aggregates the input from the vectorized map side to results that are only
> sometimes correct but mostly incorrect. HIVE-4607 tracks the proper fix, but
> meantime I'm filing a bug to disable vectorized execution if DISTINCT is
> present. Fix is trivial.
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