I just upgraded to 3.1.6 from 3.1.2. I have two plugins installed and about 20,000 members. Once I hit rebuild, the load on my dedicated server went way up with a big spike in context switches. It's so bad that MySQL seems to be totally over loaded to the point of not being able to log in as a customer. Anyone else seeing anything like this? That rebuild has always been odd.
Switch off one of the plugins, rebuild, turn off on plugin, on off plugin and rebuild again. Should reduce the load. David