WP_Query with fields test

gistfile1.php

<?php
add_action('init', 'test_wp_query');

function test_wp_query() {

    $time_start = microtime(true);

    $query = new WP_Query([
       'nopaging' => true,
       'post_type' => 'post',
       'fields' => 'ids'
    ]);

    if ( $query->have_posts() ) {
        while( $query->have_posts()) {
            $query->the_post();
            the_ID();
        }
    }

    $time_end = microtime(true);


    //execution time of the script
    echo '<b>Total Execution Time:</b> '.$time_end;

}