[jira] [Assigned] (CALCITE-3920) Improve ORDER BY computation in Enumerable convention by exploiting LIMIT

["Stamatis Zampetakis (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/CALCITE-3920?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Stamatis Zampetakis reassigned CALCITE-3920:
--------------------------------------------

    Assignee: Thomas Rebele

> Improve ORDER BY computation in Enumerable convention by exploiting LIMIT
> -------------------------------------------------------------------------
>
>                 Key: CALCITE-3920
>                 URL: https://issues.apache.org/jira/browse/CALCITE-3920
>             Project: Calcite
>          Issue Type: Improvement
>          Components: core
>    Affects Versions: 1.22.0
>            Reporter: Stamatis Zampetakis
>            Assignee: Thomas Rebele
>            Priority: Major
>
> There are many use-cases (pagination, top-k) relying on queries with an ORDER BY clause followed by a LIMIT. 
> At the moment, the two operations are implemented independently the one from the other 
>  in the Enumerable convention. Even when we know that consumer needs only the top-10 results the sort operation will try to maintain its entire input sorted. The complexity of the sorting operation is O( n ) space and O( nlogn ) time, where n is the size of the input. 
> By implementing ORDER BY and LIMIT together there are various optimizations that can be applied to reduce the space and time complexity of the sorting algorithm.



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