presto-raptor-legacy/src/main/java/io/prestosql/plugin/raptor/legacy/RaptorPageSink.java/RaptorPageSink/appendPosition
class RaptorPageSink:        public void appendPosition(Page page, int position)
        {
            pageBuilder.declarePosition();
            for (int channel = 0; channel < page.getChannelCount(); channel++) {
                Block block = page.getBlock(channel);
                BlockBuilder blockBuilder = pageBuilder.getBlockBuilder(channel);
                pageBuilder.getType(channel).appendTo(block, position, blockBuilder);
            }

            if (pageBuilder.isFull()) {
                flushToPageBuffer();
            }
        }