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Date: Sun, 25 Jun 2017 22:29:00 +0000 (UTC)
From: "Julian Hyde (JIRA)" <jira@apache.org>
To: dev@phoenix.apache.org
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Subject: [jira] [Commented] (PHOENIX-3390) Custom UDAF for HyperLogLogPlus
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archived-at: Sun, 25 Jun 2017 22:29:04 -0000


    [ https://issues.apache.org/jira/browse/PHOENIX-3390?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16062445#comment-16062445 ] 

Julian Hyde commented on PHOENIX-3390:
--------------------------------------

[~gjacoby], Thanks for the heads up. Even more pertinent than my data profiling work (which is about the problem of computing 2^n approximate distinct-counts simultaneously, see CALCITE-1616) is people's requirement to have fast, approximate distinct count. Druid supports various sketches, and we wish to surface them in Calcite's Druid adapter (see CALCITE-1787 theta-sketch, CALCITE-1587 top-N, CALCITE-1853 knowing when approximate count-distinct is acceptable).

Today many databases have a syntax for approximate aggregates, and unfortunately the syntaxes are rarely the same and are often too closely coupled to a particular algorithm (e.g HyperLogLog). I have logged CALCITE-1588 to introduce an {{APPROXIMATE}} clause, e.g. {{COUNT(DISTINCT customerId) APPROXIMATE (WITHIN 10 PERCENT))}}. It would be great if Phoenix wants to go with that syntax.

> Custom UDAF for HyperLogLogPlus
> -------------------------------
>
>                 Key: PHOENIX-3390
>                 URL: https://issues.apache.org/jira/browse/PHOENIX-3390
>             Project: Phoenix
>          Issue Type: New Feature
>            Reporter: Swapna Kasula
>            Assignee: Ethan Wang
>            Priority: Minor
>
> With ref # PHOENIX-2069
> Custome UDAF to aggregate/union of Hyperloglog's of a column and returns a Hyperloglog.
> select hllUnion(col1) from table;  //returns a Hyperloglog, which is the union of all hyperloglog's from all rows for column 'col1'


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