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From Jan Høydahl (JIRA) <j...@apache.org>
Subject [jira] [Updated] (SOLR-13025) SchemaSimilarityFactory fallback to LegacyBM25Similarity
Date Fri, 07 Dec 2018 10:26:00 GMT

     [ https://issues.apache.org/jira/browse/SOLR-13025?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Jan Høydahl updated SOLR-13025:
-------------------------------
    Description: 
This is a follow-up of LUCENE-8563: Lucene changed its BM25Similarity implementation to no
longer multiply all scores by (k1 + 1). Solr was left unchanged by replacing uses of BM25Similarity
with LegacyBM25Similarity which returns the same scores as in 7.x.

This Jira makes the default similarity depend on {{luceneMatchVersion}} for back-compat if
schema either does not define a similarity of defines {{SchemaSimilarityFactory}}. If a user
has explicitly defined {{BM25SimilarityFactory}} then the new will be used and she will need
to replace with {{LegacyBM25SimilarityFactory}} if she wants to keep old absolute scores (most
often not necessary).

This change is also described in RefGuide and CHANGES.

  was:This is a follow-up of LUCENE-8563: Lucene changed its BM25Similarity implementation
to no longer multiply all scores by (k1 + 1). Solr was left unchanged by replacing uses of
BM25Similarity with LegacyBM25Similarity which returns the same scores as in 7.x. However
it would be nice to switch back to BM25Similarity, either all the time with a note in the
migration guide, or based on the luceneMatchVersion of the collection.


> SchemaSimilarityFactory fallback to LegacyBM25Similarity
> --------------------------------------------------------
>
>                 Key: SOLR-13025
>                 URL: https://issues.apache.org/jira/browse/SOLR-13025
>             Project: Solr
>          Issue Type: Task
>      Security Level: Public(Default Security Level. Issues are Public) 
>          Components: search
>    Affects Versions: master (8.0)
>            Reporter: Adrien Grand
>            Assignee: Jan Høydahl
>            Priority: Blocker
>             Fix For: master (8.0)
>
>
> This is a follow-up of LUCENE-8563: Lucene changed its BM25Similarity implementation
to no longer multiply all scores by (k1 + 1). Solr was left unchanged by replacing uses of
BM25Similarity with LegacyBM25Similarity which returns the same scores as in 7.x.
> This Jira makes the default similarity depend on {{luceneMatchVersion}} for back-compat if
schema either does not define a similarity of defines {{SchemaSimilarityFactory}}. If a user
has explicitly defined {{BM25SimilarityFactory}} then the new will be used and she will need
to replace with {{LegacyBM25SimilarityFactory}} if she wants to keep old absolute scores (most
often not necessary).
> This change is also described in RefGuide and CHANGES.



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