BugFIx: FIxed Advance() API implementation in Optimized Composite Searchers

Author: CascadingRadium

index/scorch/optimize.go

@@ -393,5 +393,7 @@ func (i *IndexSnapshot) unadornedTermFieldReader(
 		includeNorm:        false,
 		includeTermVectors: false,
 		recycle:            false,
+		// signal downstream that this is a special unadorned termFieldReader
+		unadorned: true,
 	}
 }

index/scorch/snapshot_index_tfr.go

@@ -50,6 +50,7 @@ type IndexSnapshotTermFieldReader struct {
 	recycle            bool
 	bytesRead          uint64
 	ctx                context.Context
+	unadorned          bool
 }
 
 func (i *IndexSnapshotTermFieldReader) incrementBytesRead(val uint64) {
@@ -146,14 +147,31 @@ func (i *IndexSnapshotTermFieldReader) Advance(ID index.IndexInternalID, preAllo
 	// FIXME do something better
 	// for now, if we need to seek backwards, then restart from the beginning
 	if i.currPosting != nil && bytes.Compare(i.currID, ID) >= 0 {
-		i2, err := i.snapshot.TermFieldReader(nil, i.term, i.field,
-			i.includeFreq, i.includeNorm, i.includeTermVectors)
-		if err != nil {
-			return nil, err
+		// Check if the TFR is a special unadorned composite optimization.
+		// Such a TFR will NOT have a valid `term` or `field` set, making it
+		// impossible for the TFR to replace itself with a new one.
+		if !i.unadorned {
+			i2, err := i.snapshot.TermFieldReader(nil, i.term, i.field,
+				i.includeFreq, i.includeNorm, i.includeTermVectors)
+			if err != nil {
+				return nil, err
+			}
+			// close the current term field reader before replacing it with a new one
+			_ = i.Close()
+			*i = *(i2.(*IndexSnapshotTermFieldReader))
+		} else {
+			// unadorned composite optimization
+			// we need to reset all the iterators
+			// back to the beginning, which effectively
+			// achives the same thing as the above
+			for _, iter := range i.iterators {
+				optimizedIterator, ok := iter.(*unadornedPostingsIteratorBitmap)
+				if !ok {
+					return nil, fmt.Errorf("unexpected iterator type %T", iter)
+				}
+				optimizedIterator.ResetIterator()
+			}
 		}
-		// close the current term field reader before replacing it with a new one
-		_ = i.Close()
-		*i = *(i2.(*IndexSnapshotTermFieldReader))
 	}
 	num, err := docInternalToNumber(ID)
 	if err != nil {

index/scorch/unadorned.go

@@ -96,6 +96,12 @@ func (i *unadornedPostingsIteratorBitmap) ReplaceActual(actual *roaring.Bitmap)
 	i.actual = actual.Iterator()
 }
 
+// Resets the iterator to the beginning of the postings list.
+// by resetting the actual iterator.
+func (i *unadornedPostingsIteratorBitmap) ResetIterator() {
+	i.actual = i.actualBM.Iterator()
+}
+
 func newUnadornedPostingsIteratorFromBitmap(bm *roaring.Bitmap) segment.PostingsIterator {
 	return &unadornedPostingsIteratorBitmap{
 		actualBM: bm,