MB-61985: Add a Scorch event for Index() (#2054)

- Add a scorch event for notifying listeners, if available, that a
document is about to get added to the index, using the Index() API.
- This event can be useful for halting indexing before the Index()
operation is carried out - since Index() converts an interface into a
Document object using the IndexMapping's MapDocument, which consumes
some extra memory.
- Shifted the EventKindBatchIntroductionStart event to before the
documents were analyzed as document analysis consumes extra memory.

index.go

@@ -46,6 +46,9 @@ func (b *Batch) Index(id string, data interface{}) error {
 	if id == "" {
 		return ErrorEmptyID
 	}
+	if eventIndex, ok := b.index.(index.EventIndex); ok {
+		eventIndex.FireIndexEvent()
+	}
 	doc := document.NewDocument(id)
 	err := b.index.Mapping().MapDocument(doc, data)
 	if err != nil {

index/scorch/event.go

@@ -67,3 +67,7 @@ var EventKindMergeTaskIntroduction = EventKind(8)
 // EventKindPreMergeCheck is fired before the merge begins to check if
 // the caller should proceed with the merge.
 var EventKindPreMergeCheck = EventKind(9)
+
+// EventKindIndexStart is fired when Index() is invoked which
+// creates a new Document object from an interface using the index mapping.
+var EventKindIndexStart = EventKind(10)

index/scorch/scorch.go

@@ -49,7 +49,7 @@ type Scorch struct {
 
 	unsafeBatch bool
 
-	rootLock             sync.RWMutex
+	rootLock sync.RWMutex
 
 	root                 *IndexSnapshot // holds 1 ref-count on the root
 	rootPersisted        []chan error   // closed when root is persisted
@@ -376,6 +376,8 @@ func (s *Scorch) Delete(id string) error {
 func (s *Scorch) Batch(batch *index.Batch) (err error) {
 	start := time.Now()
 
+	// notify handlers that we're about to index a batch of data
+	s.fireEvent(EventKindBatchIntroductionStart, 0)
 	defer func() {
 		s.fireEvent(EventKindBatchIntroduction, time.Since(start))
 	}()
@@ -434,9 +436,6 @@ func (s *Scorch) Batch(batch *index.Batch) (err error) {
 
 	indexStart := time.Now()
 
-	// notify handlers that we're about to introduce a segment
-	s.fireEvent(EventKindBatchIntroductionStart, 0)
-
 	var newSegment segment.Segment
 	var bufBytes uint64
 	stats := newFieldStats()
@@ -878,3 +877,8 @@ func (s *Scorch) CopyReader() index.CopyReader {
 	s.rootLock.Unlock()
 	return rv
 }
+
+// external API to fire a scorch event (EventKindIndexStart) externally from bleve
+func (s *Scorch) FireIndexEvent() {
+	s.fireEvent(EventKindIndexStart, 0)
+}

index_impl.go

@@ -256,6 +256,8 @@ func (i *indexImpl) Index(id string, data interface{}) (err error) {
 		return ErrorIndexClosed
 	}
 
+	i.FireIndexEvent()
+
 	doc := document.NewDocument(id)
 	err = i.m.MapDocument(doc, data)
 	if err != nil {
@@ -1112,3 +1114,16 @@ func (f FileSystemDirectory) GetWriter(filePath string) (io.WriteCloser,
 	return os.OpenFile(filepath.Join(string(f), dir, file),
 		os.O_RDWR|os.O_CREATE, 0600)
 }
+
+func (i *indexImpl) FireIndexEvent() {
+	// get the internal index implementation
+	internalIndex, err := i.Advanced()
+	if err != nil {
+		return
+	}
+	// check if the internal index implementation supports events
+	if internalEventIndex, ok := internalIndex.(index.EventIndex); ok {
+		// fire the Index() event
+		internalEventIndex.FireIndexEvent()
+	}
+}