When a page is renamed or deleted, the PageNotFoundAction is called, which in turn calls the PageManager. This class finds pages that are similar to the original page in other spaces, and in doing hits the database hard, specifically the cwd_groups and spaces tables.
This results in the CPU of the database spiking, making Confluence completely inaccessible.
Edit the <confluence_install>/confluence/pages/alternativepages.vm to exclude the call to the template that renders the list of suggestions. Remove the following from that file: