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Every time I call WP_Query() in the function below, Wordpress leaks 8 megs of memory. And since I call this function a lot, things get hairy pretty quickly... :( I've tried unsetting the resulting $queryObject as well as periodically calling wp_cache_flush(), but neither seems to have any effect. Any thoughts?

function get_post_ids_in_taxonomies($taxonomies, &$terms=array()) {
    $post_ids = array();

    $query = gen_query_get_posts_in_taxonomies($taxonomies, $terms);
    // var_dump($query);

    //Perform the query
    $queryObject = new WP_Query($query); //*****THE 8 MEGABYTES IS LEAKED HERE*****

    //For all posts found...
    if($queryObject->have_posts()) {
        while($queryObject->have_posts()) {

            //Get the $post_id by capturing the output of the_ID()
            $post_id = (int) ob_get_contents();

            // echo $post_id."\n";
            $post_ids[] = $post_id;


    return $post_ids;

gen_query_get_posts_in_taxonomies() is:

function gen_query_get_posts_in_taxonomies($taxonomies, &$terms=array()) {
    //General query params
    $query = array(
        'posts_per_page'    => -1,  //Get all posts (no paging)
        'tax_query'             => array('relation' => 'OR'),

    //Add the specific taxonomies and terms onto $query['tax_query']
    foreach($taxonomies as $tax) {
        //Get terms in the taxonomies if we haven't yet
        if(!array_key_exists($tax, $terms)) {
            $terms[$tax] = array();

            $terms_tmp = get_terms($tax);
            foreach($terms_tmp as $tt)
                $terms[$tax][] = $tt->term_taxonomy_id;

        $query['tax_query'][] = array(
            'taxonomy' => $tax,
            'terms' => $terms[$tax],
            'field' => 'term_taxonomy_id',

    return $query;
share|improve this question
Have you tried the DEBUG BAR plugin? – kaiser Jun 1 '12 at 9:12
how many posts is fetched by WP_Query if your case (when 8mb is leaked)? – Eugene Manuilov Jun 3 '12 at 10:08
up vote 10 down vote accepted

Excellent responses on WP Hackers: http://lists.automattic.com/pipermail/wp-hackers/2012-June/043213.html

What you're doing with that query, is loading EVERY matching post into memory, including the full post contents. As you can imagine, this is probably quite a lot of items.

You can pass 'fields' => 'ids' into WP_Query to simply return a list of matching post_ids instead, which should reduce the memory (and processing time) significantly:


share|improve this answer

Stumbled upon this while researching the memory issue pointed out here.

In this case, you can use get_the_id instead of using buffering to capture the id, and you could narrow the queried fields to only include ids.

share|improve this answer
Thanks for the response, Thomas! I just ended up writing some raw SQL, as I recall. However, this probably would have worked too. Thanks so much! :) – rinogo Aug 26 '12 at 15:17

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