presto-raptor-legacy/src/main/java/io/prestosql/plugin/raptor/legacy/storage/OrcPageSource.java/OrcPageSource/block
class OrcPageSource:        @Override
        public Block block(Page sourcePage, long filePosition)
        {
            int count = sourcePage.getPositionCount();
            BlockBuilder builder = BIGINT.createFixedSizeBlockBuilder(count);
            for (int i = 0; i < count; i++) {
                BIGINT.writeLong(builder, filePosition + i);
            }
            return builder.build();
        }