presto-parquet/src/main/java/io/prestosql/parquet/reader/PageReader.java/PageReader/PageReader
class PageReader:    public PageReader(CompressionCodecName codec, List<DataPage> compressedPages, DictionaryPage compressedDictionaryPage)
    {
        this.codec = codec;
        this.compressedPages = new LinkedList<>(compressedPages);
        this.compressedDictionaryPage = compressedDictionaryPage;
        int count = 0;
        for (DataPage page : compressedPages) {
            count += page.getValueCount();
        }
        this.valueCount = count;
    }