[jira] [Created] (LUCENE-9103) WANDScorer can miss some hits

["Adrien Grand (Jira)" <ji...@apache.org>]

Adrien Grand created LUCENE-9103:
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             Summary: WANDScorer can miss some hits
                 Key: LUCENE-9103
                 URL: https://issues.apache.org/jira/browse/LUCENE-9103
             Project: Lucene - Core
          Issue Type: Bug
            Reporter: Adrien Grand
             Fix For: 8.4


I found the issue while building the release candidate for 8.4. There is a rare bug in WANDScorer that occurs when a block is ignored because the sum of the maximum scores is less than the minimum competitive score. In that case WANDScorer advances until it finds a block where the sum of the maximum scores is greater than the minimum competitive score. Then it pops clauses from the tail until the maximum score of the tail gets smaller than the minimum competitive score, advances these clauses beyond the current target, and treats the smallest doc ID as the next candidate. This is where the bug lies: sometimes this candidate will be beyond the current block and WANDScorer won't update maximum scores of other clauses. In this case it might skip over hits thinking that they can't have a competitive score when in fact they could.



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