Bug Fix: Handle multi-part lists properly in ReadPostingList

posting/list.go

@@ -1133,7 +1133,6 @@ func (l *List) findPosting(readTs uint64, uid uint64) (found bool, pos *pb.Posti
 // Facets gives facets for the posting representing value.
 func (l *List) Facets(readTs uint64, param *pb.FacetParams, langs []string,
 	listType bool) ([]*pb.Facets, error) {
-
 	l.RLock()
 	defer l.RUnlock()
 

posting/mvcc.go

@@ -33,6 +33,9 @@ import (
 var (
 	// ErrTsTooOld is returned when a transaction is too old to be applied.
 	ErrTsTooOld = errors.Errorf("Transaction is too old")
+	// ErrInvalidKey is returned when trying to read a posting list using
+	// an invalid key (e.g the key to a single part of a larger multi-part list).
+	ErrInvalidKey = errors.Errorf("cannot read posting list from this key")
 )
 
 // ShouldAbort returns whether the transaction should be aborted.
@@ -141,6 +144,16 @@ func unmarshalOrCopy(plist *pb.PostingList, item *badger.Item) error {
 // Use forward iterator with allversions enabled in iter options.
 // key would now be owned by the posting list. So, ensure that it isn't reused elsewhere.
 func ReadPostingList(key []byte, it *badger.Iterator) (*List, error) {
+	pk, err := x.Parse(key)
+	if err != nil {
+		return nil, errors.Wrapf(err, "while reading posting list with key [%v]", key)
+	}
+	if pk.HasStartUid {
+		// Trying to read a single part of a multi part list. This type of list
+		// should be read once using the canonical list (with startUid equal to zero).
+		return nil, ErrInvalidKey
+	}
+
 	l := new(List)
 	l.key = key
 	l.plist = new(pb.PostingList)
@@ -166,6 +179,17 @@ func ReadPostingList(key []byte, it *badger.Iterator) (*List, error) {
 				return nil, err
 			}
 			l.minTs = item.Version()
+
+			// If this list is a multi-part list, advance past the keys holding the parts.
+			if len(l.plist.GetSplits()) > 0 {
+				lastKey, err := x.GetSplitKey(key, math.MaxUint64)
+				if err != nil {
+					return nil, errors.Wrapf(err,
+						"while advancing past the end of multi-part list with key [%v]", key)
+				}
+				it.Seek(lastKey)
+			}
+
 			// No need to do Next here. The outer loop can take care of skipping
 			// more versions of the same key.
 			return l, nil