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From "Ethan Wang (JIRA)" <j...@apache.org>
Subject [jira] [Assigned] (PHOENIX-4164) APPROX_COUNT_DISTINCT becomes imprecise at 20m unique values.
Date Wed, 06 Sep 2017 05:58:00 GMT

     [ https://issues.apache.org/jira/browse/PHOENIX-4164?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Ethan Wang reassigned PHOENIX-4164:
-----------------------------------

    Assignee: Ethan Wang

> APPROX_COUNT_DISTINCT becomes imprecise at 20m unique values.
> -------------------------------------------------------------
>
>                 Key: PHOENIX-4164
>                 URL: https://issues.apache.org/jira/browse/PHOENIX-4164
>             Project: Phoenix
>          Issue Type: Bug
>            Reporter: Lars Hofhansl
>            Assignee: Ethan Wang
>
> {code}
> 0: jdbc:phoenix:localhost> select count(*) from test;
> +-----------+
> | COUNT(1)  |
> +-----------+
> | 26931816  |
> +-----------+
> 1 row selected (14.604 seconds)
> 0: jdbc:phoenix:localhost> select approx_count_distinct(v1) from test;
> +----------------------------+
> | APPROX_COUNT_DISTINCT(V1)  |
> +----------------------------+
> | 17221394                   |
> +----------------------------+
> 1 row selected (21.619 seconds)
> {code}
> The table is generated from random numbers, and the cardinality of v1 is close to the
number of rows.
> (I cannot run a COUNT(DISTINCT(v1)), as it uses up all memory on my machine and eventually
kills the regionserver - that's another story and another jira)
> [~aertoria]



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