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