apache / apache/lucene

Remove ClassicSimilarity? [LUCENE-7377]

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legacy-jira-priority:Minor type:task
Dominant language
Java
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Description

ClassicSimilarity was relying on coordination factors in order to produce good scores. Now that coords are gone, it is quite a bad option compared to eg. BM25Similarity.

Maybe we should remove ClassicSimilarity entirely in master and deprecated in 6.x in order to encourage users to move to BM25Similarity rather than stay on a Similarity impl of lesser quality?

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Migrated from [LUCENE-7377](https://issues.apache.org/jira/browse/LUCENE-7377) by Adrien Grand (@jpountz)

Contributor guide

Open the contributing guide

Research direction

Start by reviewing the ClassicSimilarity and BM25Similarity implementations and the surrounding Lucene similarity API. Determine whether the intended outcome is removal in master, deprecation in 6.x, or both; done requires a documented compatibility decision and corresponding project changes.

Written by the indexing model from the issue text.

Assessment

Tech stack
java
Domain
search
Issue type
Refactor
Difficulty
5/5
Estimated time
Over a week
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
35/100

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