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From "Ethan Wang (JIRA)" <j...@apache.org>
Subject [jira] [Comment Edited] (PHOENIX-153) Implement TABLESAMPLE clause
Date Mon, 26 Jun 2017 05:17:00 GMT

    [ https://issues.apache.org/jira/browse/PHOENIX-153?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16062546#comment-16062546
] 

Ethan Wang edited comment on PHOENIX-153 at 6/26/17 5:16 AM:
-------------------------------------------------------------

Valid Point. 

In addition, by design, this coarse problem gets magnified when three things happen (and vice
versa):
1, Table is too small
2, Guidepost width set too wide, or even no stats collected at all
3, User specifies to not use stats table for parallelization. 

Based on the observation from the testing on a table with 400K rows and GUIDE_POSTS_WIDTH
=10KB or 200KB, the sampled size was usually around +-5% of expected size. This performance
gets better and better when the GuidePosts used are more granular (Detailed chart attached.)


!Sampling_Accuracy_Performance.jpg|thumbnail!


was (Author: aertoria):
Valid Point. 

In addition, by design, this coarse problem gets magnified when three things happen (and vice
versa):
1, Table is too small
2, Guidepost width set too wide, or even no stats collected at all
3, User specifies to not use stats table for parallelization. 

Based on the observation from the testing on a table with 400K rows and GUIDE_POSTS_WIDTH
=10KB or 200KB, the sampled size was usually around +-5% of expected size. This performance
gets better and better when the GuidePosts used are more granular (Detailed chart attached.)

> Implement TABLESAMPLE clause
> ----------------------------
>
>                 Key: PHOENIX-153
>                 URL: https://issues.apache.org/jira/browse/PHOENIX-153
>             Project: Phoenix
>          Issue Type: Task
>            Reporter: James Taylor
>            Assignee: Ethan Wang
>              Labels: enhancement
>         Attachments: Sampling_Accuracy_Performance.jpg
>
>
> Support the standard SQL TABLESAMPLE clause by implementing a filter that uses a skip
next hint based on the region boundaries of the table to only return n rows per region.



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