WordPress网站文章非常多时，解决数据库查询使网站非常慢的问题

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WordPress的文章数量超过10万会明显感觉网站查询效率下降

WordPress在查询post时，默认会同时把文章数量也查询出来
当post数量到10w+时，query_posts和WP_Query会因为SQL_CALC_FOUND_ROWS出现慢查询
慢查询SQL语句为
SELECT SQL_CALC_FOUND_ROWS wp_posts.ID FROM wp_posts WHERE 1=1 AND wp_posts.post_type = 'post' AND (wp_posts.post_status = 'publish' ) ORDER BY wp_posts.post_date DESC LIMIT 0, 20
SELECT FOUND_ROWS()

解决办法：
方法一、彻底禁用SQL_CALC_FOUND_ROWS
add_action('pre_get_posts', 'wndt_post_filter');
function wndt_post_filter($query) {
if (is_admin() or !$query->is_main_query()) {
return $query;
}

// 禁止查询 SQL_CALC_FOUND_ROWS
$query->set('no_found_rows', true);
}
方法二、如果仍然需要查询文章数量，使用更加高效的EXPLAIN方式代替SQL_CALC_FOUND_ROWS

if ( ! function_exists( 'maizi_set_no_found_rows' ) ) {
/**
* 设置WP_Query的 'no_found_rows' 属性为true，禁用SQL_CALC_FOUND_ROWS
*
* @param WP_Query $wp_query WP_Query实例
* @return void
*/
function maizi_set_no_found_rows(\WP_Query $wp_query)
{
$wp_query->set('no_found_rows', true);
}
}
add_filter( 'pre_get_posts', 'maizi_set_no_found_rows', 10, 1 );

if ( ! function_exists( 'maizi_set_found_posts' ) ) {
/**
* 使用 EXPLAIN 方式重构
*/
function maizi_set_found_posts($clauses, \WP_Query $wp_query)
{
// Don't proceed if it's a singular page.
if ($wp_query->is_singular()) {
return $clauses;
}

global $wpdb;

$where = isset($clauses['where']) ? $clauses['where'] : '';
$join = isset($clauses['join']) ? $clauses['join'] : '';
$distinct = isset($clauses['distinct']) ? $clauses['distinct'] : '';

$wp_query->found_posts = (int)$wpdb->get_row("EXPLAIN SELECT $distinct * FROM {$wpdb->posts} $join WHERE 1=1 $where")->rows;

$posts_per_page = (!empty($wp_query->query_vars['posts_per_page']) ? absint($wp_query->query_vars['posts_per_page']) : absint(get_option('posts_per_page')));

$wp_query->max_num_pages = ceil($wp_query->found_posts / $posts_per_page);

return $clauses;
}
}
add_filter( 'posts_clauses', 'maizi_set_found_posts', 10, 2 );

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