Exhausted memory limit with very simple WP_Query

Question

I'm trying to display a list of posts from a certain category that I can paginate through. Since I've read that get_posts() doesn't support pagination but WP_Query does, I'm using the latter.

Here's my query:

    $mainPosts = new WP_Query(array(
      'post_type'        => 'post',
      'posts_per_page'   => 1,
      'category_name'    => 'main',
    ));

I originally has posts_per_page set to 10, but I've set to 1. No matter what I try, I get an error similar to the following:

Fatal error: Allowed memory size of 268435456 bytes exhausted (tried to allocate 140513280 bytes) in /app/public/wp-includes/functions.php on line 3730

I understand that this would happen if I am trying to pull thousands of posts or performing some kind of very expensive query, but this category has a total of 5-6 posts. I can print_r the returned object and see that it's only pulling the single post that I specified.

I should note that this only occurs if I try to run while ($mainPosts->have_posts()) { ... }.

Here's the full code of what I am doing with the query:

if ($mainPosts->have_posts()) {

    while ($mainPosts->have_posts()) {
        $postItemImage = the_post_thumbnail_url();
        $postPermalink = the_permalink();
        $postTitle = the_title();
        $postDay = the_date('F jS Y');
        $postExcerpt = the_excerpt();

        echo "<div class='row post-item'><div class='col-6 post-item-left'>
                        <div class='post-item-image' style='background-image:url(\"{$postItemImage}\")'></div></div>
                        <div class='col-6 post-item-detail'><h3>{$postTitle}</h3><div class='post-item-detail-header'>{$postDay}</div>
                        <div class='post-item-detail-main'>{$postExcerpt}</div><a href='{$postPermalink}'>Read more</a></div></div>";

    }
}

What am I doing wrong here and how can I list the few posts using WP_Query without having this memory allocation issue?

Edit: I've found that using a break; seems to resolve the memory allocation issue, however this is of course undesirable if I intend to run the loop more than once.

Answer 1

Your query looks OK, so I doubt that it will cause any problems. But then... Let's take a look at your loop:

if ($mainPosts->have_posts()) {

    while ($mainPosts->have_posts()) {
        $postItemImage = the_post_thumbnail_url();
        ...    
        echo "...";

    }
}

First of all you don't have any else in there, so there is no point in this if. But there is even bigger problem with this loop...

It will be an infinite loop, because there is no $mainPosts->the_post(), so it doesn't "consume" posts, so there are always all of them when checking loop condition.

This will work fine:

while ($mainPosts->have_posts()) {
    $mainPosts->the_post();
    $postItemImage = the_post_thumbnail_url();
    ...    
    echo "...";
}

Answer 2

Probably some of your plugins use memory. If I were you, I would turn off all the plugins and try it again. Then I might try to find the plugin. On the other hand, theme with poor code might be the culprit.