Method Find

posting/lists.go:153–233

(pred []byte, filter func([]byte) bool)

}

func (lc *LocalCache) Find(pred []byte, filter func([]byte) bool) (uint64, error) {
	txn := pstore.NewTransactionAt(lc.startTs, false)
	defer txn.Discard()

	attr := string(pred)

	initKey := x.ParsedKey{
		Attr: attr,
	}
	startKey := x.DataKey(attr, 0)
	prefix := initKey.DataPrefix()

	result := &pb.List{}
	var prevKey []byte
	itOpt := badger.DefaultIteratorOptions
	itOpt.PrefetchValues = false
	itOpt.AllVersions = true
	itOpt.Prefix = prefix
	it := txn.NewIterator(itOpt)
	defer it.Close()

	for it.Seek(startKey); it.Valid(); {
		item := it.Item()
		if bytes.Equal(item.Key(), prevKey) {
			it.Next()
			continue
		}
		prevKey = append(prevKey[:0], item.Key()...)

		// Parse the key upfront, otherwise ReadPostingList would advance the
		// iterator.
		pk, err := x.Parse(item.Key())
		if err != nil {
			return 0, err
		}

		// If we have moved to the next attribute, break
		if pk.Attr != attr {
			break
		}

		if pk.HasStartUid {
			// The keys holding parts of a split key should not be accessed here because
			// they have a different prefix. However, the check is being added to guard
			// against future bugs.
			continue
		}

		switch {
		case item.UserMeta()&BitEmptyPosting > 0:
			// This is an empty posting list. So, it should not be included.
			continue
		default:
			// This bit would only be set if there are valid uids in UidPack.
			key := x.DataKey(attr, pk.Uid)
			pl, err := lc.Get(key)
			if err != nil {
				return 0, err