presto-main/src/main/java/io/prestosql/operator/MultiChannelGroupByHash.java/DictionaryLookBack/DictionaryLookBack
class DictionaryLookBack:        public DictionaryLookBack(Block dictionary)
        {
            this.dictionary = dictionary;
            this.processed = new int[dictionary.getPositionCount()];
            Arrays.fill(processed, -1);
        }