If you are hosting a WordPress site with S4 and go to the plugins page in your WP admin then you will notice that there is a tab called ‘drop-ins’ and you will also notice that there are three files listed there.
You will see that you can’t delete them, you can’t deactivate them, and you can’t edit them, so what are they?
Drop-ins are single files that are located in the wp-content of your WordPress install. They are automatically loaded on page load under certain conditions and add to or replace WordPress functions in a way that normal plugins are not able to.
In the case of the three that you are seeing by default in a WP install hosted with S4, here is what they do:
advanced-cache.php
This file is used by virtually all WordPress cache plugins. In this case it is being used by LiteSpeed cache, which auto creates it and won’t run without it.
object-cache.php
Our caching setup uses Redis as an object cache, you don’t have to do anything with it, the object cashe is automatically controlled by the LS cache plugin, and you can disable it in the settings there if you really want to. This file enables the Redis object caching.
db-error.php
By default WordPress throws up nice error pages for things like 404 (page not found) errors, but does not include a descriptive error page if there is a problem with connecting to the database. We add one of our own, so your site visitors can see what the issue is, and also so that you and our support team are automatically notified that there is a problem.
We strongly recommend leaving them as they are, they are all doing important thing and having no negative impact.
If you want to delete the db-error page then you can do that by deleting the file from the wp-content directory. If you want to get rid of the others then you will need to disable the LiteSpeed cache plugin.
Any other ‘drop-ins’ that you don’t recognise have probably been added by other plugins that you are running. If there is something that you can’t identify or think is suspicious then get in touch with support and we will help you work out what it is doing there.