fix: avoid panic when load segment with pkoracle and idforacle already exist (#36959)

relate: https://github.com/milvus-io/milvus/issues/36949

Signed-off-by: aoiasd <zhicheng.yue@zilliz.com>

internal/querynodev2/delegator/delegator.go

@@ -913,10 +913,6 @@ func NewShardDelegator(ctx context.Context, collectionID UniqueID, replicaID Uni
 
 	excludedSegments := NewExcludedSegments(paramtable.Get().QueryNodeCfg.CleanExcludeSegInterval.GetAsDuration(time.Second))
 
-	var idfOracle IDFOracle
-	if len(collection.Schema().GetFunctions()) > 0 {
-		idfOracle = NewIDFOracle(collection.Schema().GetFunctions())
-	}
 	sd := &shardDelegator{
 		collectionID:     collectionID,
 		replicaID:        replicaID,
@@ -926,7 +922,7 @@ func NewShardDelegator(ctx context.Context, collectionID UniqueID, replicaID Uni
 		segmentManager:   manager.Segment,
 		workerManager:    workerManager,
 		lifetime:         lifetime.NewLifetime(lifetime.Initializing),
-		distribution:     NewDistribution(idfOracle),
+		distribution:     NewDistribution(),
 		deleteBuffer:     deletebuffer.NewListDeleteBuffer[*deletebuffer.Item](startTs, sizePerBlock),
 		pkOracle:         pkoracle.NewPkOracle(),
 		tsafeManager:     tsafeManager,
@@ -935,7 +931,6 @@ func NewShardDelegator(ctx context.Context, collectionID UniqueID, replicaID Uni
 		factory:          factory,
 		queryHook:        queryHook,
 		chunkManager:     chunkManager,
-		idfOracle:        idfOracle,
 		partitionStats:   make(map[UniqueID]*storage.PartitionStatsSnapshot),
 		excludedSegments: excludedSegments,
 		functionRunners:  make(map[int64]function.FunctionRunner),
@@ -955,6 +950,11 @@ func NewShardDelegator(ctx context.Context, collectionID UniqueID, replicaID Uni
 		}
 	}
 
+	if len(sd.isBM25Field) > 0 {
+		sd.idfOracle = NewIDFOracle(collection.Schema().GetFunctions())
+		sd.distribution.SetIDFOracle(sd.idfOracle)
+	}
+
 	m := sync.Mutex{}
 	sd.tsCond = sync.NewCond(&m)
 	if sd.lifetime.Add(lifetime.NotStopped) == nil {

internal/querynodev2/delegator/delegator_data.go

@@ -487,7 +487,7 @@ func (sd *shardDelegator) LoadSegments(ctx context.Context, req *querypb.LoadSeg
 		})
 
 		var bm25Stats *typeutil.ConcurrentMap[int64, map[int64]*storage.BM25Stats]
-		if len(sd.isBM25Field) > 0 {
+		if sd.idfOracle != nil {
 			bm25Stats, err = sd.loader.LoadBM25Stats(ctx, req.GetCollectionID(), infos...)
 			if err != nil {
 				log.Warn("failed to load bm25 stats for segment", zap.Error(err))
@@ -690,8 +690,11 @@ func (sd *shardDelegator) loadStreamDelete(ctx context.Context,
 		sd.pkOracle.Register(candidate, targetNodeID)
 	}
 
-	if sd.idfOracle != nil {
+	if sd.idfOracle != nil && bm25Stats != nil {
 		bm25Stats.Range(func(segmentID int64, stats map[int64]*storage.BM25Stats) bool {
+			log.Info("register sealed segment bm25 stats into idforacle",
+				zap.Int64("segmentID", segmentID),
+			)
 			sd.idfOracle.Register(segmentID, stats, segments.SegmentTypeSealed)
 			return false
 		})

internal/querynodev2/delegator/distribution.go

@@ -91,7 +91,7 @@ type SegmentEntry struct {
 }
 
 // NewDistribution creates a new distribution instance with all field initialized.
-func NewDistribution(idfOracle IDFOracle) *distribution {
+func NewDistribution() *distribution {
 	dist := &distribution{
 		serviceable:     atomic.NewBool(false),
 		growingSegments: make(map[UniqueID]SegmentEntry),
@@ -100,13 +100,18 @@ func NewDistribution(idfOracle IDFOracle) *distribution {
 		current:         atomic.NewPointer[snapshot](nil),
 		offlines:        typeutil.NewSet[int64](),
 		targetVersion:   atomic.NewInt64(initialTargetVersion),
-		idfOracle:       idfOracle,
 	}
 
 	dist.genSnapshot()
 	return dist
 }
 
+func (d *distribution) SetIDFOracle(idfOracle IDFOracle) {
+	d.mut.Lock()
+	defer d.mut.Unlock()
+	d.idfOracle = idfOracle
+}
+
 func (d *distribution) PinReadableSegments(partitions ...int64) (sealed []SnapshotItem, growing []SegmentEntry, version int64, err error) {
 	d.mut.RLock()
 	defer d.mut.RUnlock()

internal/querynodev2/delegator/distribution_test.go

@@ -21,8 +21,6 @@ import (
 	"time"
 
 	"github.com/stretchr/testify/suite"
-
-	"github.com/milvus-io/milvus-proto/go-api/v2/schemapb"
 )
 
 type DistributionSuite struct {
@@ -31,7 +29,7 @@ type DistributionSuite struct {
 }
 
 func (s *DistributionSuite) SetupTest() {
-	s.dist = NewDistribution(NewIDFOracle([]*schemapb.FunctionSchema{}))
+	s.dist = NewDistribution()
 	s.Equal(initialTargetVersion, s.dist.getTargetVersion())
 }