I have attached 4 SQL scripts for generating notifications records, 1 for each supported database engine. You may wish to modify this depending on your set-up, e.g. change to mdl_ table prefix to something else. You can also increase the 4000000 number on the last line to something larger if the  "Background processing for messaging" task runs quickly enough in your environment that you can't confidently state it's faster with the index. Deploy a site without the patch. If your site has a system cron job to run scheduled tasks, disable it. Go to Site Administration -> Server -> Tasks -> Scheduled tasks. Run in the terminal: php admin/cli/scheduled_task.php --execute='\core\task\messaging_cleanup_task' Run the attached generate_notifications script that is appropriate for your database. Run in the terminal: php admin/cli/scheduled_task.php --execute='\core\task\messaging_cleanup_task' Note the time it takes to execute, "...used XXX seconds" Truncate the mdl_notifications table Re-run the generate notifications script Deploy the patch and run the upgrade to created the new indexes Run in the terminal: php admin/cli/scheduled_task.php --execute='\core\task\messaging_cleanup_task' Note the time it takes to execute, "...used YYY seconds" Confirm YYY is faster than XXX.