loop through all posts memory error

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I have few thousands posts and need to list all of them in the admin. When I used WP_Query to get them all at once I got a memory error. Then I split it into several query calls and it worked just fine with 256 MB limit. Here is the code: 

$limit = 200;
$offset = 0;
while (TRUE) {
    $posts = new WP_Query(array(
            'posts_per_page'        => $limit,
            'offset'                => $offset,
            'post_type'     =>  $post_type,
            'orderby'       =>  'title',
            'order'         =>  'ASC',
            'post_status' => array('publish', 'private', 'draft', 'inherit'),
    ));

    if (!$posts->have_posts()) break;

    while($posts->have_posts())
    {
            $posts->the_post();

            # do some echoing with the $post
    }

    $offset += $limit;
} /*(TRUE)*/

So this works just fine on development server. But when moved to production, it throws memory error Allowed memory size of 268435456 bytes exhausted (tried to allocate 64 bytes) ...

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I tried lowering the $limit but it doesn’t help (on dev it actually works just fine with $limit = 500.

What else can I do to force it to release memory?

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2 comments

  1. The posts are still held in memory under WordPress’ cache mechanism (even though you replace $posts on every loop) – delete each one after operating on it:

    # do some echoing with the $post

# wipe post from memory
wp_cache_delete( $post->ID, 'posts' );
wp_cache_delete( $post->ID, 'post_meta' );

    Pro tip: save some needless queries with no_found_rows => true in your query args.

    And if you’re not using categories/tags in your loop, save even more queries (& memory) with update_post_term_cache => false in your query args.

  2. While the above does reduce memory usage somewhat, on large loops (>2500 posts) you will still see memory usage going up with each loop.

    The following will flush all WordPress caches, making memory usage as small as possible:

    wp_cache_flush();