private boolean isVersionedUpstream(final GraphNode startSeekingNode) {
        if (root.equals(startSeekingNode)) {
            return false;
        }

        for (final GraphNode parentNode : startSeekingNode.parentNodes()) {
            // in order for this node to be versioned, all parents must be versioned
            if (!isVersionedOrVersionedUpstream(parentNode)) {
                return false;
            }
        }
        return true;
    }
Seeks up the parent chain to determine whether the input to this node is versioned,
i.e., whether the output of its parent(s) is versioned or not
streams/src/main/java/org/apache/kafka/streams/kstream/internals/InternalStreamsBuilder.java