WordPress Development

When WordPress caching system makes things slower

Last week has launch time for my/Samsys latest and last plugin, an internal messaging system for WordPress websites, developed to work together a custom WordPress product for Pre-schools.

The plugin allows registered users to exchange messages between them using a front-end interface ( non-admin users) and a back-end interface on the wp-admin (users with administrative access).

Everything was going smoothly until I started testing on a live website with more than 600 registered users. The front-end ran smoothly but the back-end became painfully slow with over 15 seconds of load time.

After some investigation, I was able to pinpoint the “problem”, multiple databases calls for “update_meta_cache” each call only took milliseconds to process but there were thousands of them and it was slowing down the back-end performance.

What’s “update_meta_cache” ?

As it’s name suggests, this functions updates metadata cache on a specified object and runs  everytime you fetch metada from the database.

“update_meta_cache” is very handy on the front-end where exists a caching mechanism in place but in the back-end, no cache is active and it slowed down the plugin performance painfully. The solution has relatively simple, instead of fetching the users every time I needed them listed I created an object with all the needed user data, saved it using Transients API, and every time a new user it’s added to the website the object it’s re-created with the new data.