If you edit your system profile -> measures -> create measure -> Server side performance -> transaction based measures -> Database -> Time. This measure "Represents the total time that has been spent by the database connection component and the database management system for database execution calls."
If you edit your system profile -> measures -> create measure and then search for "connection pool", you can find the connection pool measure that matches the technology that you use. Then you will be able to track the connection pool for your database.
If that doesn't work, then you could try using a "Custom JMX measure" to grab such details.
Also, you ever want to know what is going on behind the scenes in a built in dashlet, you have two options:
1. Hover over the column name and a description of the metric will be displayed.
2. You can also click F1 and the documentation page related to that dashlet will open up in your default browser.