I have a multisites with a shared db edit.example.com and site.example.com. They share many tables but do not share all (a work in progress to determine what exactly need to be share). For example, the system table is not shared in order to be able to control what modules need to be enabled across all, on edit.example.com only and on site.example.com only. Does this can help performance? Is this a good idea or is it just adding an extra level of unnecessary complexity?For example I see caching becoming a problem because cache_page is not shared, or even if it is shared.
If there are any references out there please refer me to it.