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https://issues.apache.org/jira/browse/LUCENE-9269?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17055901#comment-17055901
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Adrien Grand commented on LUCENE-9269:
--------------------------------------
We should remove BlendedTermQuery eventually. It tries to solve cross-field
search and synonym search at the same time, which introduces complications...
Since you seem to be using it for the synonym case, you can look at
SynonymQuery, which can deal with multiple synonyms that have different boosts
today already. For cross-field search, we have a BM25FQuery, though I hope
we'll find ways to make it easier to use in the future, e.g. by moving the
scoring logic to Similarity.
> 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
> Priority: Minor
> Attachments: LUCENE-9269-test.patch
>
>
> If two blended queries are should clauses of a boolean query and 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}
> a)
> 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
> b)
> 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
> c)
> 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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