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https://issues.apache.org/jira/browse/HIVE-17114?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16094588#comment-16094588
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Rui Li commented on HIVE-17114:
-------------------------------
{{constprog_semijoin}} needs sorting query results. Other failures are not
related. Update patch v3 to address it.
[~xuefuz], [~csun] would you mind take a look? Thanks.
The idea is to set UNIFORM trait to RS in {{SetSparkReducerParallelism}}, when
num reducers is automatically decided. Most of the code change is refactoring
in order to be more concise.
> HoS: Possible skew in shuffling when data is not really skewed
> --------------------------------------------------------------
>
> Key: HIVE-17114
> URL: https://issues.apache.org/jira/browse/HIVE-17114
> Project: Hive
> Issue Type: Bug
> Reporter: Rui Li
> Assignee: Rui Li
> Priority: Minor
> Attachments: HIVE-17114.1.patch, HIVE-17114.2.patch,
> HIVE-17114.3.patch
>
>
> Observed in HoS and may apply to other engines as well.
> When we join 2 tables on a single int key, we use the key itself as hash code
> in {{ObjectInspectorUtils.hashCode}}:
> {code}
> case INT:
> return ((IntObjectInspector) poi).get(o);
> {code}
> Suppose the keys are different but are all some multiples of 10. And if we
> choose 10 as #reducers, the shuffle will be skewed.
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