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https://issues.apache.org/jira/browse/PHOENIX-846?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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James Taylor resolved PHOENIX-846.
----------------------------------
Resolution: Fixed
Fix Version/s: 5.0.0
4.0.0
3.0.0
Assignee: James Taylor
> Select DISTINCT with LIMIT does full scans
> ------------------------------------------
>
> Key: PHOENIX-846
> URL: https://issues.apache.org/jira/browse/PHOENIX-846
> Project: Phoenix
> Issue Type: Bug
> Affects Versions: 3.0.0, 4.0.0
> Reporter: alex kamil
> Assignee: James Taylor
> Priority: Critical
> Fix For: 3.0.0, 4.0.0, 5.0.0
>
> Attachments: PHOENIX-846.patch
>
>
> When running SELECT DISTINCT with LIMIT it does full scan and aggregation (no
> pageFilter/limit used on server side),
> this severely affects performance (query returns in 20sec vs 300ms without
> DISTINCT)
> : jdbc:phoenix:localhost> explain select DISTINCT ROWKEY from TEST_1M LIMIT
> 100;
> +------------+
> | PLAN |
> +------------+
> | CLIENT PARALLEL 30-WAY FULL SCAN OVER TEST_1M |
> | SERVER FILTER BY FIRST KEY ONLY |
> | SERVER AGGREGATE INTO ORDERED DISTINCT ROWS BY [ROWKEY] |
> | CLIENT MERGE SORT |
> | CLIENT 100 ROW LIMIT |
> +------------+
> -------------------------------------------------
> for comparison SELECT without DISTINCT uses a limit PageFilter=100 on server
> side and doesn't do full scan (query returns in 300ms)
> explain select ROWKEY from TEST_1M LIMIT 100;
> +------------+
> | PLAN |
> +------------+
> | CLIENT PARALLEL 30-WAY FULL SCAN OVER TEST_1M |
> | SERVER FILTER BY FIRST KEY ONLY AND PageFilter 100 |
> | CLIENT MERGE SORT |
> | CLIENT 100 ROW LIMIT |
> +------------+
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