[jira] [Created] (LUCENE-9269) Blended queries with boolean rewrite can result in inconstitent scores

["Michele Palmia (Jira)" <ji...@apache.org>]

Michele Palmia created LUCENE-9269:
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             Summary: Blended queries with boolean rewrite can result in inconstitent scores
                 Key: LUCENE-9269
                 URL: https://issues.apache.org/jira/browse/LUCENE-9269
             Project: Lucene - Core
          Issue Type: Bug
          Components: core/search
    Affects Versions: 8.4
            Reporter: Michele Palmia


If two blended queries are built so that
 * some of their terms are the same
 * their rewrite method is BlendedTermQuery.BOOLEAN_REWRITE

the docFreq for the overlapping terms used for scoring is picked as follow:
 * if the overlapping terms are not boosted, the df of the term in the first blended query is used
 * if any of the overlapping terms is boosted, the df is picked at (what looks like) random.

A few examples using a field with 2 terms: f:a (df: 2), and f:b (df: 3).

 
{code:java}
1.
Blended(f:a f:b) Blended (f:a)
        df: 3             df: 2
gets rewritten to:
(f:a)^2.0 (f:b)
df: 3      df:2

Blended(f:a) Blended(f:a f:b)
        df: 2        df: 3
gets rewritten to:
(f:a)^2.0 (f:b)
 df: 2     df:2

Blended(f:a f:b^0.66) Blended (f:a^0.75)
        df: 3                  df: 2
gets rewritten to:
(f:a)^1.75 (f:b)^0.66
 df:?       df:2
{code}
with ? either 2 or 3, depending on the run.

 



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