presto-main/src/main/java/io/prestosql/operator/LookupJoinPageBuilder.java/LookupJoinPageBuilder/appendRow
class LookupJoinPageBuilder:    public void appendRow(JoinProbe probe, LookupSource lookupSource, long joinPosition)
    {
        // probe side
        appendProbeIndex(probe);

        // build side
        buildPageBuilder.declarePosition();
        lookupSource.appendTo(joinPosition, buildPageBuilder, 0);
    }