presto-main/src/main/java/io/prestosql/operator/index/PageRecordSet.java/PageRecordCursor/getSlice
class PageRecordCursor:        @Override
        public Slice getSlice(int field)
        {
            checkState(position >= 0, "Not yet advanced");
            checkState(position < page.getPositionCount(), "Already finished");
            Type type = types.get(field);
            return type.getSlice(page.getBlock(field), position);
        }