This is the number of connections created over time, not the number of currently active connections - that should never go over 200 based on you settings.

Example: your app opens a connection and 100 connections are created. Then the app asks for more connections. At some point the app reaches 200 connections. Then everyone goes to lunch and the number of connections drops down to 100. Everyone comes back from lunch and the app is busy and you again have 200 connections. Total connections create at this point is 300.

One other point - if there is no app activity, and the connection timeout happens, the existing 100 connections will be dropped and 100 new connections opened (there was another post about this - a search for "postgresql connection" should turn it up). Thus even in a system that is not doing anything you can see the total number of connections created increase.

Erratic? Possibly. I doubt that you would ever be in a situation where 200 connections get used and are in use continually. You would have to monitor the in use connection count for a period of time to determine the exact usage pattern.

If you want to only ever create 200 connections, then set min and max to the same. Then as long as you don't run into the timeout situation I mentioned earlier, there should be a total of 200 connections created over time.