presto-spi/src/main/java/io/prestosql/spi/Page.java/Page/toString
class Page:    @Override
    public String toString()
    {
        StringBuilder builder = new StringBuilder("Page{");
        builder.append("positions=").append(positionCount);
        builder.append(", channels=").append(getChannelCount());
        builder.append('}');
        builder.append("@").append(Integer.toHexString(System.identityHashCode(this)));
        return builder.toString();
    }