Comment by 8ytecoder

This is at the very least a clever and involved optimization. Let me tell you the story of my similar 10h to 10min fix. We had this cronjob that was supposed to run every hour, detect all changes to the customers and related table and sync with the marketing saas tool. It was written in Rails and took 10 mins at first. As we grew the time taken by this job also grew linearly. To a point where it took 10 hours and we could only sync the data twice a day. As it turns out the job was loading each user and then scanning for changes. We switched it into a somewhat complex sql query and MySQL ran it in a few mins. Add the additional processing and the whole job now took 10 mins.