• The domain is now "org.mongodb.driver", whereas it used to be "com.mongodb".
• The full ObjectName is:
  • org.mongodb.driver:type=ConnectionPool,host=<host>,port=<port>,instance=<unique instance number for the host and port>
• The Name attribute has been dropped
• The remaining attributes are:
  • Host
  • Port
  • MinSize
  • MaxSize
  • Total
  • InUse

In the 3.0 architecture, there is no way to support the ConnectionPoolStatisticsBean from the 2.x MXBean version, so it's been dropped. May add something equivalent, but in a different MBean, at a later date.