presto-main/src/main/java/io/prestosql/operator/OuterLookupSource.java/OuterLookupSource/appendTo
class OuterLookupSource:    @Override
    public void appendTo(long position, PageBuilder pageBuilder, int outputChannelOffset)
    {
        lookupSource.appendTo(position, pageBuilder, outputChannelOffset);
        outerPositionTracker.positionVisited(position);
    }