[jira] [Updated] (HIVE-17114) HoS: Possible skew in shuffling when data is not really skewed

["Rui Li (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/HIVE-17114?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Rui Li updated HIVE-17114:
--------------------------
    Attachment: HIVE-17114.1.patch

I think we can set the UNIFORM trait to the RS and then MurmurHash is used to compute the hash code, which can solve the issue here.

> 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
>
>
> 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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