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https://issues.apache.org/jira/browse/PHOENIX-418?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16110419#comment-16110419
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Hadoop QA commented on PHOENIX-418:
-----------------------------------
{color:red}-1 overall{color}. Here are the results of testing the latest
attachment
http://issues.apache.org/jira/secure/attachment/12879968/PHOENIX-418-v1.patch
against master branch at commit 5e33dc12bc088bd0008d89f0a5cd7d5c368efa25.
ATTACHMENT ID: 12879968
{color:green}+1 @author{color}. The patch does not contain any @author
tags.
{color:green}+1 tests included{color}. The patch appears to include 4 new
or modified tests.
{color:red}-1 patch{color}. The patch command could not apply the patch.
Console output:
https://builds.apache.org/job/PreCommit-PHOENIX-Build/1242//console
This message is automatically generated.
> Support approximate COUNT DISTINCT
> ----------------------------------
>
> Key: PHOENIX-418
> URL: https://issues.apache.org/jira/browse/PHOENIX-418
> Project: Phoenix
> Issue Type: Task
> Reporter: James Taylor
> Assignee: Ethan Wang
> Labels: gsoc2016
> Attachments: PHOENIX-418-v1.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).
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