Github user jelmerterwal commented on the issue:

    https://github.com/apache/tomcat/pull/54
  
    For an application I develop, I see a drop in connections. The screenshot 
show different values of the connection pool.
    
    Legend for the colours;
    - grey -> pool size
    - greenish -> idle connections
    - orange/red -> connections in use
    - purple -> waiting for a connection
    
    ![screen shot 2017-04-24 at 13 49 
43](https://cloud.githubusercontent.com/assets/5363087/25335835/07a5554c-28f5-11e7-97f4-d877f1181e50.png)
    
    The application uses dropwizard (www.dropwizard.io) which internally uses 
Tomcat's JDBC Pool. The application has 4 instances. The graph shows the sum of 
these instances for the number of connections.
    
    - min size of idle connection is set to 10 (so should be 10 x 4 = 40)
    - the decrease happens due abandoning of connections
    
    The documentation indicates a minimum pool of idle connections should be 
available. It scared me when I first saw this happening.
    
    ```
    minIdle
    
    (int) The minimum number of established connections that should be kept in 
the pool at all times. The connection pool can shrink below this number if 
validation queries fail. Default value is derived from initialSize:10 (also see 
testWhileIdle)
    ```



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