The wp_oembed_get() function is not cached by default. Unfortunately, many themes (like Elegant Themes Divi) still use it which leads to your page making many background requests to YouTube and similar video embedding sites. This slows down your pageloads since WordPress has to wait for YouTube to response before showing your page.

If you’re not able to fix your theme, you can add the code below into an mu-plugin or into your themes functions.php file. It will cache embeds that are using wp_oembed_get(). Please note that embeds that fail to resolve (for example: deleted youtube video) will still not be cached. This is due to the way wp_oembed_get() works internally and is not trivial to fix.

<?php
/**
 * Cache wp_oembed_get()
 * Version: 1.0
 */

define('CUSTOM_OEMBED_CACHE_KEY', 'coc_');

function _wp_custom_oembed_cache_key($url, $args) {
  $args_serialized = serialize($args);
  return CUSTOM_OEMBED_CACHE_KEY . md5("{$url}-{$args_serialized}");
}

/**
 * This function caches the result
 */
add_filter('oembed_result', function($data, $url, $args) {
  // Cache result
  set_transient(_wp_custom_oembed_cache_key($url, $args), $data, DAY_IN_SECONDS);
  return $data;
}, 999, 3);

/**
 * This function serves the cached result
 */
add_filter('pre_oembed_result', function($result, $url, $args) {

  // Clean out empty oembed calls caused by Divi
  if(trim($url) === '') {
    return '';
  }

  // Return cached result if available
  if($cached_result = get_transient(_wp_custom_oembed_cache_key($url, $args))) {
    return $cached_result;
  }

  return $result;
}, 2, 3);

By default, WordPress sends a maximum of one email per day to the site administrator if a fatal error is discovered. (Since WordPress 5.2)

To configure this, use the following snippet:

add_filter('recovery_mode_email_rate_limit', function($rate) {
  return HOUR_IN_SECONDS;
});

Instead of using one of the predefined constants like HOUR_IN_SECONDS, you can use any integer value, like 600, which would correspond to every 10 minutes.

WordPress 5.2 pioneered a new “Recovery mode” feature that can notify site administrators by email if their site experiences a fatal error.

By default, the email is sent to either an email configured under the RECOVERY_MODE_EMAIL constant or the user that created the website (admin_email option).

If you want this email to multiple addresses, you can use the snippet below in your themes functions.php or in a plugin. Configure the extra address on line 6.

add_filter('recovery_mode_email', function($email, $url) {
  $email_array = [];
  $email_array[] = $email['to'];

  // Adds another email
  $email_array[] = 'your-email@gmail.com';

  $email['to'] = $email_array;

  return $email;
}, 10, 2);

A query to list authors / users by post count:

SELECT wp_users.ID, wp_users.user_nicename, COUNT(*) as count FROM wp_posts, wp_users WHERE wp_posts.post_type='post' AND wp_posts.post_status='publish' AND wp_posts.post_author = wp_users.ID GROUP BY post_author ORDER BY count DESC LIMIT 5 ;

Resulting table:

ID,user_nicename,count
29,"user-a",18
66,"user-b",16
26,"user-c",10
24,"user-f",9
48,"user-z",6