Add BM25 k3 query-term frequency saturation to classic query parser#15818
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sgup432 wants to merge 3 commits intoapache:mainfrom
Open
Add BM25 k3 query-term frequency saturation to classic query parser#15818sgup432 wants to merge 3 commits intoapache:mainfrom
sgup432 wants to merge 3 commits intoapache:mainfrom
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Description
Related issue - #15768
Adds BM25 k3 parameter to the classic query parser for query-side term frequency saturation. Duplicate terms in a query string now get their boost computed as ((k3+1)*qtf)/(k3+qtf) instead of linear summing, when enabled via
parser.setK3(8f).Defaults to -1 (disabled) — fully backward compatible. Saturation is applied at parse time in QueryParserBase.getBooleanQuery() so BooleanQuery.rewrite() never sees duplicates.
Example:
Query: "pizza pizza pizza restaurant" with k3 = 8
Without k3 (current behavior — linear boost via BooleanQuery.rewrite()):
With parser.setK3(8f) — saturated at parse time:
The weight 2.4545 comes from ((8+1)*3)/(8+3) = 27/11. Repeating a term gives diminishing returns instead of scaling linearly.