Samuel Wood (Otto) on "High CPU Load After Update to v4.3"

After reading through that ticket, I can see this being the cause of extreme load in some cases. Here's how to fix the problem. You will need shell or file access to the server.

Step 1. Fix the actual issue by applying part of the patch in that ticket. It's a one liner. Open the wp-includes/taxonomy.php file, and go to line 4448. This is that line:

wp_schedule_single_event( 'wp_batch_split_terms', time() + MINUTE_IN_SECONDS );

The problem is that the arguments are reversed. Switch them, like so:

wp_schedule_single_event( time() + MINUTE_IN_SECONDS, 'wp_batch_split_terms' );

That will fix the underlying issue, but it won't stop the load. To do that, we're going to make a temporary mu-plugin.

Step 2. Navigate to your /wp-content directory. Create a subdirectory called "mu-plugins", at /wp-content/mu-plugins. The name of the directory is important. If you already have that directory, just go in there.

MU Plugins are "must use". All PHP files in this directory get auto-included by WordPress. It's a handy way to run some code in your WordPress instance without having access to the Plugin page to activate plugins.

Create a new file called "fix.php". Or anything, the name doesn't matter. This will be the contents of that file:

<?php
function clear_bad_cron_entries() {
    // Fix incorrect cron entries for term splitting
    $cron_array = _get_cron_array();
    if ( isset( $cron_array['wp_batch_split_terms'] ) ) {
        foreach ( $cron_array['wp_batch_split_terms'] as $timestamp_hook => $cron_data ) {
            foreach ( $cron_data as $key => $args ) {
                wp_unschedule_event( 'wp_batch_split_terms', $timestamp_hook, $args['args'] );
            }
        }
    }
}
clear_bad_cron_entries();

This is the same code in 4.3.1 to clean up the problem. You need it to run now instead. So paste that code into the fix.php file, and save.

Now, navigate to your site. The problem should clear up shortly. Once it does, you can delete the fix.php file. It only needs to run once, not every time your site loads.

If you are using multi-site, then you need to load every site at least once to allow this code to run on all of them. Cron jobs are stored per-site, not per-instance.