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

["Ruben Q L (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CALCITE-3920?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17170682#comment-17170682 ] 

Ruben Q L edited comment on CALCITE-3920 at 8/5/20, 8:10 AM:
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Thanks for the clarification [~thomas.rebele], sorry for the misunderstanding (even if a certain test execution with PriorityQueue can be stable, depending on the input set, generally there is no guarantee for that).
I guess we must decide if it is required to have a stable solution (via an ad-hoc algorithm, I guess) or not (via PriorityQueue). In my opinion it is desirable to have a stable algorithm, it will help with the predictability of the operator (and will simplify testing).
 


was (Author: rubenql):
Thanks for the clarification [~thomas.rebele], sorry for the misunderstanding (even if a certain test execution with PriorityQueue can be stable, depending on the input set, generally there is no guarantee for that).
I guess we must decide if it is required to have a stable solution (via an ad-hoc algorithm, I guess) or not (via PriorityQueue, ). In my opinion it is desirable to have a stable algorithm, it will help with the predictability of the operator (and will simplify testing).
 

> 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
>              Labels: pull-request-available
>          Time Spent: 3h 20m
>  Remaining Estimate: 0h
>
> 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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