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How to size database max connections with openstack

We are implementing a private openstack environment, and have 3 controllers, with more compute nodes in the near future. We have glance, nova, cinder, neutron, and keystone. We have increased our database max connections from the default of 100 to 300, but still are running out of connections. We can increase that number further, but want to know if there is a reasonable formula to use. I know that all the services create worker processes, and it seems to be related to the number of cpus. For instance, one one server, we have 26 glance-registry, and 26 glance-api processes. And that is just one service.

Does anyone know of a reasonable formula or sizing document? maybe something like #cpus X 5 x number of glance controllers (just for glance connections).   Currently, looking at my database connections I have:

29 glance, 32 cinder, 130 nova, 23 neutron, and 11 keystone connections active on the db server. Any ideas on proper sizing of db connections?