[LUCENE-6887] 5x: backport ClassicSimilarity, mark DefaultSimilarity deprecated & update javadocs to mention ClassicSim vs. BM25Sim

• Type: Task
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 5.4
• Lucene Fields: New
• Assignee: Chris M. Hostetter
• Reporter: Chris M. Hostetter
• Created: 05/Nov/15 18:51
• Updated: 28/Aug/22 14:45
• Resolved: 05/Nov/15 21:35

Description

LUCENE-6789 changed the default Similarity on trunk to BM25, and renamed DefaultSimiliarity to ClassicSimilarity for backcompat w/o confusion about the "default" name.

But nothing related to this change was committed to the 5x branch.

On the 5x branch we should:

• mark DefaultSimiliarity deprecated
• provide a ClassicSimilarity for 5.x users to switch to to resolve deprecations w/o changing behavior (and allow smooth upgrade to 6.x later)
• note in the DefaultSimiliarity javadocs that starting with 6.0 BM25 will be the recommended default and users should investigate it

Issue Links

• blocks: SOLR-8239 Deprecate/rename DefaultSimilarityFactory to ClassicSimilarityFactory and remove DefaultSimilarityFactory in trunk
• relates to: LUCENE-6789 change IndexSearcher default similarity to BM25