presto-main/src/main/java/io/prestosql/operator/JoinHash.java/JoinHash/startJoinPosition
class JoinHash:    private long startJoinPosition(int currentJoinPosition, int probePosition, Page allProbeChannelsPage)
    {
        if (currentJoinPosition == -1) {
            return -1;
        }
        if (positionLinks == null) {
            return currentJoinPosition;
        }
        return positionLinks.start(currentJoinPosition, probePosition, allProbeChannelsPage);
    }