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Posted to issues@spark.apache.org by "Michael Armbrust (JIRA)" <ji...@apache.org> on 2015/09/15 23:25:46 UTC

[jira] [Resolved] (SPARK-5030) Approximated cardinality with HyperLogLog UDAF

     [ https://issues.apache.org/jira/browse/SPARK-5030?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Michael Armbrust resolved SPARK-5030.
-------------------------------------
    Resolution: Duplicate

> Approximated cardinality with HyperLogLog UDAF
> ----------------------------------------------
>
>                 Key: SPARK-5030
>                 URL: https://issues.apache.org/jira/browse/SPARK-5030
>             Project: Spark
>          Issue Type: New Feature
>          Components: SQL
>            Reporter: XIAO Pin
>            Priority: Minor
>   Original Estimate: 672h
>  Remaining Estimate: 672h
>
> HyperLogLog  is a good way to improve performance of cardinality calculate(count distinct), especially in the case of skew data. Of course, there will be some loss of accuracy：
> select hllc(a) from test_tbl group by b



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