As far as I know, one WordPress Multisite installation has one global php memory limit. This is done on the server level via php.ini.
Your Multisite users to install and test random plugins? That’s a pretty major security issue. As the installation administrator you install a bunch of secure and applicable plugins and then you can let your users pick what they want to have activated.
Also, Mutlsite is designed for a set of sites for a community of users. I would highly recommend not using Multisite in your scenario.
No, end users are unable to install new plugins, and we provide that bunch of very well tested, multisite compatible, plugins. Those plugins covers a wide range of requirements and end users receive their new sites with those plugins deactivated, so they enable what they need. The problem is with several admins of different websites, who enabled lots of plugins that they don’t actually use or need, and it stay active, generating a great memory usage. I thought about limiting what plugins can they access to, but it only generate a huge flow of customer support queries.
If I could provide only 64 MB for most users, and expand their memory limit when they really need it, we could optimize memory usage.
The solution we found by now, is to maintain two multisite installs in the same server, so they can start using a limited amount of RAM (64 MB), and if they develop to a more important project, they are migrated to the multisite with 128 MB of usable memory. If their potential of growth is too good, they are moved to an individual WP install. This work for us, yet it means keeping up with two multisite installs.
BTW, we use a cache plugin, mysql cache, CDN, and all the posible optimizations to do their user experience as smooth as posible.
Any thoughts regarding this scenario could come in handy.
Well no. Because PHP is per server user, not per WP instance. PHP has the memory, or it doesn’t. WP isn’t smart enough to know, it’s all PHP 🙂
The solution is
1) Get more memory
2) Remove/limit usage of the plugins that cause the problem.
ok, that’s what I was afraid of. Thank you for the clarifications.