MB-62182: bug fixes in the fast merge path

index.go

@@ -401,3 +401,8 @@ type TrainableIndex interface {
 	Index
 	Train(*Batch) error
 }
+
+type IndexFileCopyable interface {
+	SetPathInBolt(key []byte, value []byte) error       //dest index
+	CopyFile(file string, d index.IndexDirectory) error // source index
+}

index/scorch/persister.go

@@ -895,10 +895,6 @@ func zapFileName(epoch uint64) string {
 	return fmt.Sprintf("%012x.zap", epoch)
 }
 
-func (s *Scorch) loadTrainedData(bucket *bolt.Bucket) error {
-	return s.trainer.loadTrainedData(bucket)
-}
-
 // bolt snapshot code
 
 func (s *Scorch) loadFromBolt() error {

index/scorch/scorch.go

@@ -20,6 +20,7 @@ import (
 	"io"
 	"os"
 	"path/filepath"
+	"strconv"
 	"sync"
 	"sync/atomic"
 	"time"
@@ -470,6 +471,24 @@ func (s *Scorch) Delete(id string) error {
 	return s.Batch(b)
 }
 
+func (s *Scorch) isTrained(batch *index.Batch) (bool, error) {
+	trained := true
+	if len(batch.IndexOps) > 0 && s.trainer != nil {
+		val, err := s.getInternal(util.BoltTrainCompleteKey)
+		if err != nil {
+			return false, err
+		}
+
+		if val != nil {
+			trained, err = strconv.ParseBool(string(val))
+			if err != nil {
+				return false, err
+			}
+		}
+	}
+	return trained, nil
+}
+
 // Batch applices a batch of changes to the index atomically
 func (s *Scorch) Batch(batch *index.Batch) (err error) {
 	start := time.Now()
@@ -480,6 +499,15 @@ func (s *Scorch) Batch(batch *index.Batch) (err error) {
 		s.fireEvent(EventKindBatchIntroduction, time.Since(start))
 	}()
 
+	trained, err := s.isTrained(batch)
+	if err != nil {
+		return err
+	}
+
+	if !trained {
+		return fmt.Errorf("index is not trained yet")
+	}
+
 	resultChan := make(chan index.Document, len(batch.IndexOps))
 
 	var numUpdates uint64

index/scorch/stats.go

@@ -136,6 +136,9 @@ type Stats struct {
 	MaxMemMergeZapTime      uint64
 	TotMemMergeSegments     uint64
 	TotMemorySegmentsAtRoot uint64
+
+	TotTrainedSamples uint64
+	TotTrainTime      uint64
 }
 
 // atomically populates the returned map