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Ethan Wang edited comment on PHOENIX-418 at 8/25/17 3:03 AM: ------------------------------------------------------------- Local run was OK (a few IT fails, re run OK, like usual). I'll monitor the pre-commit run for v6 patch Running on java version "1.8.0_102" with {code:java} mvn -fae install -DnumForkedIT=3 {code} was (Author: aertoria): Local run was OK (a few IT fails, re run OK, like usual). I'll monitor the pre-commit run for v6 patch > 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, PHOENIX-418-v2.patch, > PHOENIX-418-v3.patch, PHOENIX-418-v4.patch, PHOENIX-418-v5.patch, > PHOENIX-418-v6.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). -- This message was sent by Atlassian JIRA (v6.4.14#64029)