Why my Tomcat 9 does not keep the jdbc connections open as it is specified in minIdle?

Question

I have configured my Tomcat 9 to keep a database pool using the server.xml in order to have a minimum of 50 connections to my mysql database. When the tomcat starts I can see all the connections there with the command SHOW PROCESSLIST. I can't figure out why after a couple of days I only see 8 connections.

This is my configuration. I have included parameters whose name has changed along different tomcat versions, for example maxActive and maxTotal, to ensure that the parameter value is taken.

    <Resource
        name="MySqlDS"
        auth="Container"
        type="javax.sql.DataSource"
        driverClassName="com.mysql.jdbc.Driver"
        factory="org.apache.tomcat.jdbc.pool.DataSourceFactory"
        url="jdbc:mysql://localhost:3306/MYDB?zeroDateTimeBehavior=convertToNull"
        username=*****
        password=*****
        initialSize="50"
        maxActive="100"
        maxTotal="100"
        minIdle="50"
        maxIdle="100"
        maxWaitMillis="10000"
        maxWait="10000"
        maxAge="0"
        minEvictableIdleTimeMillis="60000"
        timeBetweenEvictionRunsMillis="30000"
        suspectTimeout="60"
        validationQuery="SELECT 1"
        validationInterval="30000"
        testOnBorrow="true"
        removeAbandoned="true"
        removeAbandonedOnBorrow="true"
        removeAbandonedOnMaintenance="true"
        removeAbandonedTimeout="60"
        logAbandoned="true"
    />

What can be happening? It's my configuration wrong?

I use mysql-connector-java-5.1.13 and OpenJDK 1.8.0_275

Answer 1

I solved the issue adding this parameter:

testWhileIdle="true"