presto-orc/src/main/java/io/prestosql/orc/DictionaryCompressionOptimizer.java/DictionaryCompressionOptimizer/getIndexBytesPerRow
class DictionaryCompressionOptimizer:        public double getIndexBytesPerRow()
        {
            checkState(!directEncoded);
            return 1.0 * getIndexBytes() / rowCount;
        }