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Posted to issues@spark.apache.org by "Zhenhua Wang (JIRA)" <ji...@apache.org> on 2017/10/12 15:10:02 UTC
[jira] [Commented] (SPARK-22164) support histogram in estimating
the cardinality of aggregate (or group-by) operator
[ https://issues.apache.org/jira/browse/SPARK-22164?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16202081#comment-16202081 ]
Zhenhua Wang commented on SPARK-22164:
--------------------------------------
[~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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