presto-main/src/main/java/io/prestosql/operator/MultiChannelGroupByHash.java/AddRunLengthEncodedPageWork/process
class AddRunLengthEncodedPageWork:        @Override
        public boolean process()
        {
            checkState(!finished);
            if (page.getPositionCount() == 0) {
                finished = true;
                return true;
            }

            // needRehash() == false indicates we have reached capacity boundary and a rehash is needed.
            // We can only proceed if tryRehash() successfully did a rehash.
            if (needRehash() && !tryRehash()) {
                return false;
            }

            // Only needs to process the first row since it is Run Length Encoded
            putIfAbsent(0, page);
            finished = true;

            return true;
        }