fix: force to set the metric type in the search request (#36279)

- issue: #35960
- pr: #35962

Signed-off-by: SimFG <bang.fu@zilliz.com>

internal/querycoordv2/task/executor.go

@@ -366,6 +366,8 @@ func (ex *Executor) subscribeChannel(task *ChannelTask, step int) error {
 		partitions...,
 	)
 
+	ex.setMetricTypeForMetaInfo(loadMeta, indexInfo)
+
 	dmChannel := ex.targetMgr.GetDmChannel(task.CollectionID(), action.ChannelName(), meta.NextTarget)
 	if dmChannel == nil {
 		msg := "channel does not exist in next target, skip it"
@@ -738,4 +740,5 @@ func (ex *Executor) setMetricTypeForMetaInfo(metaInfo *querypb.LoadMetaInfo, ind
 			}
 		}
 	}
+	log.Warn("metric type not found in index info, set it to default", zap.Any("indexInfos", indexInfos), zap.Any("metaInfo", metaInfo))
 }

internal/querynodev2/segments/collection.go

@@ -40,6 +40,7 @@ import (
 	"github.com/milvus-io/milvus/pkg/common"
 	"github.com/milvus-io/milvus/pkg/log"
 	"github.com/milvus-io/milvus/pkg/metrics"
+	"github.com/milvus-io/milvus/pkg/util/funcutil"
 	"github.com/milvus-io/milvus/pkg/util/indexparamcheck"
 	"github.com/milvus-io/milvus/pkg/util/paramtable"
 	"github.com/milvus-io/milvus/pkg/util/typeutil"
@@ -143,7 +144,8 @@ type Collection struct {
 	// but Collection in Manager will be released before assign new replica of new resource group on these node.
 	// so we don't need to update resource group in Collection.
 	// if resource group is not updated, the reference count of collection manager works failed.
-	metricType atomic.String // deprecated
+	// Deprecated
+	metricType *atomic.String
 	schema     atomic.Pointer[schemapb.CollectionSchema]
 	isGpuIndex bool
 	loadFields typeutil.Set[int64]
@@ -161,6 +163,12 @@ func (c *Collection) GetResourceGroup() string {
 	return c.resourceGroup
 }
 
+// Deprecated
+// GetMetricType it'll deprecate in the 2.5.x, please don't use it
+func (c *Collection) GetMetricType() string {
+	return c.metricType.Load()
+}
+
 // ID returns collection id
 func (c *Collection) ID() int64 {
 	return c.id
@@ -281,6 +289,7 @@ func NewCollection(collectionID int64, schema *schemapb.CollectionSchema, indexM
 		refCount:      atomic.NewUint32(0),
 		isGpuIndex:    isGpuIndex,
 		loadFields:    loadFieldIDs,
+		metricType:    atomic.NewString(GetMetricType(schema, indexMeta)), // only for compatibility of rolling upgrade from 2.3.x to 2.4
 	}
 	for _, partitionID := range loadMetaInfo.GetPartitionIDs() {
 		coll.partitions.Insert(partitionID)
@@ -290,6 +299,27 @@ func NewCollection(collectionID int64, schema *schemapb.CollectionSchema, indexM
 	return coll
 }
 
+func GetMetricType(schema *schemapb.CollectionSchema, indexMeta *segcorepb.CollectionIndexMeta) string {
+	vecField, err := typeutil.GetVectorFieldSchema(schema)
+	if err != nil {
+		log.Warn("get vector field failed", zap.String("collection", schema.GetName()), zap.Error(err))
+		return ""
+	}
+	vecIndexMeta, ok := lo.Find(indexMeta.GetIndexMetas(), func(fieldIndexMeta *segcorepb.FieldIndexMeta) bool {
+		return fieldIndexMeta.GetFieldID() == vecField.GetFieldID()
+	})
+	if !ok || vecIndexMeta == nil {
+		log.Warn("cannot find index info for field", zap.String("field", vecField.GetName()), zap.String("collection", schema.GetName()))
+		return ""
+	}
+	metricType, err := funcutil.GetAttrByKeyFromRepeatedKV(common.MetricTypeKey, vecIndexMeta.GetIndexParams())
+	if err != nil {
+		log.Warn("get metric type failed", zap.String("collection", schema.GetName()), zap.Error(err))
+		return ""
+	}
+	return metricType
+}
+
 func NewCollectionWithoutSchema(collectionID int64, loadType querypb.LoadType) *Collection {
 	return &Collection{
 		id:         collectionID,

internal/querynodev2/services.go

@@ -648,6 +648,7 @@ func (node *QueryNode) SearchSegments(ctx context.Context, req *querypb.SearchRe
 		zap.Int64("collectionID", req.Req.GetCollectionID()),
 		zap.String("channel", channel),
 		zap.String("scope", req.GetScope().String()),
+		zap.Any("metric_type", req.GetReq().GetMetricType()),
 	)
 	channelsMvcc := make(map[string]uint64)
 	for _, ch := range req.GetDmlChannels() {
@@ -751,6 +752,9 @@ func (node *QueryNode) Search(ctx context.Context, req *querypb.SearchRequest) (
 		resp.Status = merr.Status(merr.WrapErrCollectionNotFound(req.GetReq().GetCollectionID()))
 		return resp, nil
 	}
+	if req.Req.MetricType == "" {
+		req.Req.MetricType = collection.GetMetricType()
+	}
 
 	toReduceResults := make([]*internalpb.SearchResults, len(req.GetDmlChannels()))
 	runningGp, runningCtx := errgroup.WithContext(ctx)