presto-raptor-legacy/src/main/java/io/prestosql/plugin/raptor/legacy/RaptorPageSink.java/RaptorPageSink/getBucketArgsPage
class RaptorPageSink:        private Page getBucketArgsPage(Page page)
        {
            Block[] blocks = new Block[bucketFields.length];
            for (int i = 0; i < bucketFields.length; i++) {
                blocks[i] = page.getBlock(bucketFields[i]);
            }
            return new Page(page.getPositionCount(), blocks);
        }