snapshot of https://github.com/blevesearch/bleve.git (master, 2026-09-15; blobs > 131072B omitted)

rescorer.go

@@ -0,0 +1,160 @@
+//  Copyright (c) 2025 Couchbase, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// 		http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package bleve
+
+import (
+	"github.com/blevesearch/bleve/v2/fusion"
+	"github.com/blevesearch/bleve/v2/search"
+	"github.com/blevesearch/bleve/v2/search/query"
+)
+
+const (
+	DefaultScoreRankConstant = 60
+)
+
+// Rescorer is applied after all the query and knn results are obtained.
+// The main use of Rescorer is in hybrid search; all the individual scores
+// for query and knn are combined using Rescorer. Makes use of algorithms
+// defined in `fusion`
+type rescorer struct {
+	req *SearchRequest
+
+	// Stores the original From, Size and Boost parameters from the request
+	origFrom   int
+	origSize   int
+	origBoosts []float64
+
+	// Flag variable to make sure that restoreSearchRequest is only run once
+	// when it is deferred
+	restored bool
+}
+
+// Stores information about the hybrid search into FusionRescorer.
+// Also mutates the SearchRequest by:
+// - Setting boosts to 1: top level boosts only used for rescoring
+// - Setting From and Size to 0 and ScoreWindowSize
+func (r *rescorer) prepareSearchRequest() error {
+	if r.req.Params == nil {
+		r.req.Params = NewDefaultParams(r.req.From, r.req.Size)
+	}
+
+	r.origFrom = r.req.From
+	r.origSize = r.req.Size
+
+	r.req.From = 0
+	r.req.Size = r.req.Params.ScoreWindowSize
+
+	// req.Query's top level boost comes first, followed by the KNN queries
+	numQueries := numKNNQueries(r.req) + 1
+	r.origBoosts = make([]float64, numQueries)
+
+	// only modify queries if it is boostable. If not, ignore
+	if bQuery, ok := r.req.Query.(query.BoostableQuery); ok {
+		r.origBoosts[0] = bQuery.Boost()
+		bQuery.SetBoost(1.0)
+	} else {
+		r.origBoosts[0] = 1.0
+	}
+
+	// for all the knn queries, replace boost values
+	r.prepareKnnRequest()
+
+	return nil
+}
+
+func (r *rescorer) restoreSearchRequest() {
+	// Skip if already restored
+	if r.restored {
+		return
+	}
+	r.restored = true
+
+	r.req.From = r.origFrom
+	r.req.Size = r.origSize
+
+	if bQuery, ok := r.req.Query.(query.BoostableQuery); ok {
+		bQuery.SetBoost(r.origBoosts[0])
+	}
+
+	// for all the knn queries, restore boost values
+	r.restoreKnnRequest()
+}
+
+func (r *rescorer) rescore(ftsHits, knnHits search.DocumentMatchCollection) (search.DocumentMatchCollection, uint64, float64) {
+	mergedHits := r.mergeDocs(ftsHits, knnHits)
+
+	var fusionResult *fusion.FusionResult
+
+	switch r.req.Score {
+	case ScoreRRF:
+		fusionResult = fusion.ReciprocalRankFusion(
+			mergedHits,
+			r.origBoosts,
+			r.req.Params.ScoreRankConstant,
+			r.req.Params.ScoreWindowSize,
+			numKNNQueries(r.req),
+			r.req.Explain,
+		)
+	case ScoreRSF:
+		fusionResult = fusion.RelativeScoreFusion(
+			mergedHits,
+			r.origBoosts,
+			r.req.Params.ScoreWindowSize,
+			numKNNQueries(r.req),
+			r.req.Explain,
+		)
+	}
+
+	return fusionResult.Hits, fusionResult.Total, fusionResult.MaxScore
+}
+
+// Merge all the FTS and KNN docs along with explanations
+func (r *rescorer) mergeDocs(ftsHits, knnHits search.DocumentMatchCollection) search.DocumentMatchCollection {
+	if len(knnHits) == 0 {
+		return ftsHits
+	}
+
+	knnHitMap := make(map[string]*search.DocumentMatch, len(knnHits))
+
+	for _, hit := range knnHits {
+		knnHitMap[hit.ID] = hit
+	}
+
+	for _, hit := range ftsHits {
+		if knnHit, ok := knnHitMap[hit.ID]; ok {
+			hit.ScoreBreakdown = knnHit.ScoreBreakdown
+			if r.req.Explain {
+				hit.Expl = &search.Explanation{Value: 0.0, Message: "", Children: append([]*search.Explanation{hit.Expl}, knnHit.Expl.Children...)}
+			}
+			delete(knnHitMap, hit.ID)
+		}
+	}
+
+	for _, hit := range knnHitMap {
+		hit.Score = 0
+		ftsHits = append(ftsHits, hit)
+		if r.req.Explain {
+			hit.Expl = &search.Explanation{Value: 0.0, Message: "", Children: append([]*search.Explanation{nil}, hit.Expl.Children...)}
+		}
+	}
+
+	return ftsHits
+}
+
+func newRescorer(req *SearchRequest) *rescorer {
+	return &rescorer{
+		req: req,
+	}
+}