JMX integrations such as Cassandra, Tomcat, Kafka, etc. can potentially generate thousands of metrics and by default, these integrations are limited to 350. If you'd like this number increased, please email email@example.com.
To check the current metric list, run the JMX list_everything command that is provided via the agent:
sudo /etc/init.d/datadog-agent jmx list_everything
To list attributes that do match one of your instances configuration but that are not being collected because it would exceed the number of metrics collected:
sudo /etc/init.d/datadog-agent jmx list_limited_attributes