[jira] [Resolved] (LUCENE-10196) Improve IntroSorter with 3-ways partitioning

["Bruno Roustant (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/LUCENE-10196?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Bruno Roustant resolved LUCENE-10196.
-------------------------------------
    Fix Version/s: 8.11
       Resolution: Fixed

Thanks reviewers!

> Improve IntroSorter with 3-ways partitioning
> --------------------------------------------
>
>                 Key: LUCENE-10196
>                 URL: https://issues.apache.org/jira/browse/LUCENE-10196
>             Project: Lucene - Core
>          Issue Type: Improvement
>            Reporter: Bruno Roustant
>            Priority: Major
>             Fix For: 8.11
>
>          Time Spent: 2h
>  Remaining Estimate: 0h
>
> I added a SorterBenchmark to evaluate the performance of the various Sorter implementations depending on the strategies defined in BaseSortTestCase (random, random-low-cardinality, ascending, descending, etc).
> By changing the implementation of the IntroSorter to use a 3-ways partitioning, we can gain a significant performance improvement when sorting low-cardinality lists, and with additional changes we can also improve the performance for all the strategies.
> Proposed changes:
>  - Sort small ranges with insertion sort (instead of binary sort).
>  - Select the quick sort pivot with medians.
>  - Partition with the fast Bentley-McIlroy 3-ways partitioning algorithm.
>  - Replace the tail recursion by a loop.



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