enhance: [2.5] weighted reranker to allow skip score normalization (#40905)

issue: https://github.com/milvus-io/milvus/issues/40836
pr: https://github.com/milvus-io/milvus/pull/40903

Signed-off-by: Buqian Zheng <zhengbuqian@gmail.com>

internal/proxy/reScorer.go

@@ -77,12 +77,18 @@ func (rs *rrfScorer) scorerType() rankType {
 
 type weightedScorer struct {
 	baseScorer
-	weight float32
+	weight    float32
+	normScore bool
 }
 
 type activateFunc func(float32) float32
 
 func (ws *weightedScorer) getActivateFunc() activateFunc {
+	if !ws.normScore {
+		return func(distance float32) float32 {
+			return distance
+		}
+	}
 	mUpper := strings.ToUpper(ws.getMetricType())
 	isCosine := mUpper == strings.ToUpper(metric.COSINE)
 	isIP := mUpper == strings.ToUpper(metric.IP)
@@ -190,6 +196,11 @@ func NewReScorers(ctx context.Context, reqCnt int, rankParams []*commonpb.KeyVal
 		if _, ok := params[WeightsParamsKey]; !ok {
 			return nil, errors.New(WeightsParamsKey + " not found in rank_params")
 		}
+		// normalize scores by default
+		normScore := true
+		if _, ok := params[NormScoreKey]; ok {
+			normScore = params[NormScoreKey].(bool)
+		}
 		weights := make([]float32, 0)
 		switch reflect.TypeOf(params[WeightsParamsKey]).Kind() {
 		case reflect.Slice:
@@ -210,7 +221,7 @@ func NewReScorers(ctx context.Context, reqCnt int, rankParams []*commonpb.KeyVal
 			return nil, errors.New("The weights param should be an array")
 		}
 
-		log.Debug("weights params", zap.Any("weights", weights))
+		log.Debug("weights params", zap.Any("weights", weights), zap.Bool("norm_score", normScore))
 		if reqCnt != len(weights) {
 			return nil, merr.WrapErrParameterInvalid(fmt.Sprint(reqCnt), fmt.Sprint(len(weights)), "the length of weights param mismatch with ann search requests")
 		}
@@ -219,7 +230,8 @@ func NewReScorers(ctx context.Context, reqCnt int, rankParams []*commonpb.KeyVal
 				baseScorer: baseScorer{
 					scorerName: "weighted",
 				},
-				weight: weights[i],
+				weight:    weights[i],
+				normScore: normScore,
 			}
 		}
 	default:

internal/proxy/reScorer_test.go

@@ -104,9 +104,29 @@ func TestRescorer(t *testing.T) {
 		assert.Contains(t, err.Error(), "rank param weight should be in range [0, 1]")
 	})
 
+	t.Run("weights with norm_score false", func(t *testing.T) {
+		weights := []float64{0.5, 0.2}
+		params := make(map[string]interface{})
+		params[WeightsParamsKey] = weights
+		params[NormScoreKey] = false
+		b, err := json.Marshal(params)
+		assert.NoError(t, err)
+		rankParams := []*commonpb.KeyValuePair{
+			{Key: RankTypeKey, Value: "weighted"},
+			{Key: RankParamsKey, Value: string(b)},
+		}
+
+		rescorers, err := NewReScorers(context.TODO(), 2, rankParams)
+		assert.NoError(t, err)
+		assert.Equal(t, 2, len(rescorers))
+		assert.Equal(t, weightedRankType, rescorers[0].scorerType())
+		assert.Equal(t, float32(weights[0]), rescorers[0].(*weightedScorer).weight)
+		assert.False(t, rescorers[0].(*weightedScorer).normScore)
+	})
+
 	t.Run("weights", func(t *testing.T) {
 		weights := []float64{0.5, 0.2}
-		params := make(map[string][]float64)
+		params := make(map[string]interface{})
 		params[WeightsParamsKey] = weights
 		b, err := json.Marshal(params)
 		assert.NoError(t, err)
@@ -120,5 +140,7 @@ func TestRescorer(t *testing.T) {
 		assert.Equal(t, 2, len(rescorers))
 		assert.Equal(t, weightedRankType, rescorers[0].scorerType())
 		assert.Equal(t, float32(weights[0]), rescorers[0].(*weightedScorer).weight)
+		// normalize scores by default
+		assert.True(t, rescorers[0].(*weightedScorer).normScore)
 	})
 }

internal/proxy/task.go

@@ -120,6 +120,7 @@ const (
 	RankParamsKey    = "params"
 	RRFParamsKey     = "k"
 	WeightsParamsKey = "weights"
+	NormScoreKey     = "norm_score"
 )
 
 type task interface {