2018MMDD:
  AFFECTS: users of databases/{arangodb32,arangodb33,clickhouse,mariadb100-server,mariadb101-server,mariadb102-server,mariadb55-server,mongodb,mongodb32,mongodb34,mongodb34-rocks,mongodb36,mysql55-server,mysql56-server,mysql57-server,mysql80-server,mysqlwsrep56-server,mysqlwsrep57-server,percona55-server,percona56-server,percona57-server}
  AUTHOR: 0mp@FreeBSD.org

  This change only affects systems running 12-CURRENT.

  The mechanism to set service process resource limits in rc.conf(5)
  (${name}_limits) has changed.

  Many databases implement their own ways of resource control.  A popular
  implementation is defining ${name}_limits to be used and configured via
  rc.conf(5), which defaults to "NO".  If set to "YES", however, limits(1) is
  run before starting a database server service.

  The new mechanism runs limits(1) by default and uses the ${name}_limits
  variable to let the user pass extra flags to the limits(1) command.  The new
  mechanism is not backward compatible as neither "YES" nor "NO" are valid
  limits(1) flags.  As a result the service may refuse to start with an error
  message similar to "limits: NO: No such file or directory".  See rc.subr(8)
  for details.

  For example, the equivalence of the old "mongod_limits='YES'" configuration
  is now "mongod_limits='-U mongodb'".