presto-main/src/main/java/io/prestosql/operator/MultiChannelGroupByHash.java/GetNonDictionaryGroupIdsWork/GetNonDictionaryGroupIdsWork
class GetNonDictionaryGroupIdsWork:        public GetNonDictionaryGroupIdsWork(Page page)
        {
            this.page = requireNonNull(page, "page is null");
            // we know the exact size required for the block
            this.blockBuilder = BIGINT.createFixedSizeBlockBuilder(page.getPositionCount());
        }