[CALCITE-3920] Improve ORDER BY computation in Enumerable convention by exploiting LIMIT

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 1.22.0
• Fix Version/s: 1.26.0
• Component/s: core
• Labels: pull-request-available
• Assignee: Thomas Rebele
• Reporter: Stamatis Zampetakis
• Created: 13/Apr/20 14:51
• Updated: 06/Oct/20 17:16
• Resolved: 04/Sep/20 07:53

Description

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.

Issue Links

• is related to: CALCITE-4157 Use a different sort algorithm for EnumerableDefaults.orderBy(...)
• links to: GitHub Pull Request #2080
• links to: GitHub Pull Request #2109