presto-orc/src/main/java/io/prestosql/orc/writer/SliceDictionaryColumnWriter.java/SliceDictionaryColumnWriter/getIndexBytes
class SliceDictionaryColumnWriter:    @Override
    public int getIndexBytes()
    {
        checkState(!directEncoded);
        return toIntExact(estimateIndexBytesPerValue(dictionary.getEntryCount()) * getNonNullValueCount());
    }