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