I just learned today that JRun 4 Updater 1 and later have additional JRun metrics logging parameters available for monitoring datasource connections. Configured in the SERVER-INF/jrun.xml file, the metrics can be enabled in the LoggerService node, and the metrics format can be customized to log jdbc timeouts, connection pool size, active connections, query duration, and query count. The metrics format can be set to monitor these parameters globally or they can be set to monitor just specific datasources.

Note that the JRun datasource metrics are for JRun datasources only, so CFMX for JRun datasources can't be monitored this way.

For documentation on logging JRun metrics see:
Monitoring the web server connection

And for documentation on these newer datasource metrics see:
New JDBC Metrics

Be aware of one bug in the JDBC metrics reporting. The Pool Size will show double the number of initial connections on server startup and then after time as connections timeout it will show initial connections plus minimum connections as the Pool Size.