presto-main/src/main/java/io/prestosql/operator/aggregation/GenericAccumulatorFactory.java/OrderingGroupedAccumulator/addInput
class OrderingGroupedAccumulator:        @Override
        public void addInput(GroupByIdBlock groupIdsBlock, Page page)
        {
            Block[] blocks = new Block[page.getChannelCount() + 1];
            for (int i = 0; i < page.getChannelCount(); i++) {
                blocks[i] = page.getBlock(i);
            }
            // Add group id block
            blocks[page.getChannelCount()] = groupIdsBlock;
            groupCount = max(groupCount, groupIdsBlock.getGroupCount());
            pagesIndex.addPage(new Page(blocks));
        }