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Posted to issues@spark.apache.org by "Yin Huai (JIRA)" <ji...@apache.org> on 2015/12/17 07:43:46 UTC

[jira] [Commented] (SPARK-6006) Optimize count distinct in case of high cardinality columns

    [ https://issues.apache.org/jira/browse/SPARK-6006?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15061594#comment-15061594 ] 

Yin Huai commented on SPARK-6006:
---------------------------------

SPARK-12077 fixed it.

> Optimize count distinct in case of high cardinality columns
> -----------------------------------------------------------
>
>                 Key: SPARK-6006
>                 URL: https://issues.apache.org/jira/browse/SPARK-6006
>             Project: Spark
>          Issue Type: Improvement
>          Components: SQL
>    Affects Versions: 1.1.1, 1.2.1
>            Reporter: Yash Datta
>            Assignee: Davies Liu
>            Priority: Minor
>             Fix For: 1.6.0
>
>
> In case there are a lot of distinct values, count distinct becomes too slow since it tries to hash partial results to one map. It can be improved by creating buckets/partial maps in an intermediate stage where same key from multiple partial maps of first stage hash to the same bucket. Later we can sum the size of these buckets to get total distinct count.



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