[LUCENE-8343] BlendedInfixSuggester bad score calculus for certain suggestion weights

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 7.3.1
• Fix Version/s: 8.0
• Component/s: core/search
• Lucene Fields: New, Patch Available
• Assignee: Unassigned
• Reporter: Alessandro Benedetti
• Created: 01/Jun/18 11:50
• Updated: 06/Oct/21 21:57
• Resolved: 11/Sep/18 17:32

Description

Currently the BlendedInfixSuggester return a (long) score to rank the suggestions.
This score is calculated as a multiplication between :

long Weight : the suggestion weight, coming from a document field, it can be any long value ( including 1, 0,.. )

double Coefficient : 0<=x<=1, calculated based on the position match, earlier the better

The resulting score is a long, which means that at the moment, any weight<10 can bring inconsistencies.

Edge cases 
Weight =1
Score = 1( if we have a match at the beginning of the suggestion) or 0 ( for any other match)

Weight =0
Score = 0 ( independently of the position match coefficient)

Issue Links

• causes: LUCENE-10156 BlendedInfixSuggester incorrectly scores items with high and low weights
• is required by: LUCENE-8347 BlendedInfixSuggester to handle multi term matches better
• links to: GitHub Pull Request #391
• links to: GitHub Pull Request #393