[jira] [Comment Edited] (SPARK-22164) support histogram in estimating the cardinality of aggregate (or group-by) operator

["Zhenhua Wang (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/SPARK-22164?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16202081#comment-16202081 ] 

Zhenhua Wang edited comment on SPARK-22164 at 10/12/17 3:21 PM:
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[~ron8hu] I don't think we will use histogram in group-by estimation, ndv can be updated through propagation based on histogram (if any), we only need ndv here. Let's close this?


was (Author: zenwzh):
[~ron8hu] I don't think histogram can help with group-by, let's close this?

> support histogram in estimating the cardinality of aggregate (or group-by) operator
> -----------------------------------------------------------------------------------
>
>                 Key: SPARK-22164
>                 URL: https://issues.apache.org/jira/browse/SPARK-22164
>             Project: Spark
>          Issue Type: Sub-task
>          Components: SQL
>    Affects Versions: 2.2.0
>            Reporter: Ron Hu
>
> Histogram is effective in dealing with skewed distribution. After we generate histogram information for column statistics, we need to adjust aggregate (or group-by) cardinality estimation based on equi-height histogram information.



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