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https://issues.apache.org/jira/browse/SOLR-13025?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16704724#comment-16704724
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Jan Høydahl commented on SOLR-13025:
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I did an attempt at a luceneMatchVersion sensitive {{BM25SimilarityFacotry}} so
that it could create an instance of {{BM25Similarity}} in >= 8.0.0 and
{{LegacyBM25Similarity}} if < 8.0.0. But that requires the factory to be
{{SolrCoreAware}}, and the Schema API, more specifically
{{FieldTypePluginLoader}} does not support loading SolrCoreAware components. Is
there some way of determining luceneMatchVersion from the IndexSchema object?
We could as an alternative handle this fallback only for
{{SchemaSimilarityFactory}} i.e. if a similarity is not configured, which would
circumvent this, but I thought that users that defined {{<similarity
class="solr.BM25SimilarityFactory">}} might expect same behaviour for
luceneMatchVersion=7.x even after upgrading to 8.0. Wdyt?
> Replace usage of LegacyBM25Similarity with BM25Similarity
> ---------------------------------------------------------
>
> 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. 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.
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