[jira] [Created] (LUCENE-10225) Improve IntroSelector with 3-way partitioning

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

Bruno Roustant created LUCENE-10225:
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             Summary: Improve IntroSelector with 3-way partitioning
                 Key: LUCENE-10225
                 URL: https://issues.apache.org/jira/browse/LUCENE-10225
             Project: Lucene - Core
          Issue Type: Improvement
            Reporter: Bruno Roustant


The same way we improved IntroSorter, we can improve IntroSelector with Bentley-McIlroy 3-way partitioning. The gain in performance is roughly the same.

With this new approach, we always use medians-of-medians (Tukey's Ninther), so there is no real gain to fallback to a slower medians-of-medians technique as an introspective protection (like the existing implementation does). Instead we can simply shuffle the sub-range if we exceed the recursive max depth (this does not change the speed as this intro-protective mechanism almost never happens - maybe only in adversarial cases).



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