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From "Hudson (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (PHOENIX-418) Support approximate COUNT DISTINCT
Date Thu, 31 Aug 2017 02:41:01 GMT

    [ https://issues.apache.org/jira/browse/PHOENIX-418?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16148367#comment-16148367
] 

Hudson commented on PHOENIX-418:
--------------------------------

FAILURE: Integrated in Jenkins build Phoenix-master #1759 (See [https://builds.apache.org/job/Phoenix-master/1759/])
PHOENIX-418 Include APPROX_COUNT_DISTINCT in server jar for support of (jtaylor: rev 6e6c0a390b7139c5ab2541d27871dbfb9c08c059)
* (edit) pom.xml
* (edit) phoenix-core/pom.xml
* (edit) phoenix-server/pom.xml


> Support approximate COUNT DISTINCT
> ----------------------------------
>
>                 Key: PHOENIX-418
>                 URL: https://issues.apache.org/jira/browse/PHOENIX-418
>             Project: Phoenix
>          Issue Type: New Feature
>            Reporter: James Taylor
>            Assignee: Ethan Wang
>            Priority: Blocker
>              Labels: gsoc2016
>             Fix For: 4.12.0
>
>         Attachments: PHOENIX-418-v1.patch, PHOENIX-418-v2.patch, PHOENIX-418-v3.patch,
PHOENIX-418-v4.patch, PHOENIX-418-v5.patch, PHOENIX-418-v6.patch, PHOENIX-418-v6-pom.patch
>
>
> Support an "approximation" of count distinct to prevent having to hold on to all distinct
values (since this will not scale well when the number of distinct values is huge). The Apache
Drill folks have had some interesting discussions on this [here](http://mail-archives.apache.org/mod_mbox/incubator-drill-dev/201306.mbox/%3CJIRA.12650169.1369931282407.88049.1370645900553%40arcas%3E).
They recommend using  [Welford's method](http://en.wikipedia.org/wiki/Algorithms_for_calculating_variance_Online_algorithm).
I'm open to having a config option that uses exact versus approximate. I don't have experience
implementing an approximate implementation, so I'm not sure how much state is required to
keep on the server and return to the client (other than realizing it'd be much less that returning
all distinct values and their counts).
> Update:
> Syntax of using approximate count distinct as:
> select APPROX_COUNT_DISTINCT(name) from person
> select APPROX_COUNT_DISTINCT(address||name) from person
> It is equivalent of  Select COUNT(DISTINCT ID) from person. Implemented using hyperloglog,
see discuss below.
> Source code patch link below, co-authorred with [~swapna]
> https://git-wip-us.apache.org/repos/asf?p=phoenix.git;a=commitdiff;h=d6381afc3af976ccdbb874d4458ea17b1e8a1d32



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