Unable to get JDBC connection but only 10% of available connections are being used

问题

Here is exception I am getting

This is the configuration I am using in my c3p0

<property name="acquireIncrement">5</property>
        <property name="preferredTestQuery">SELECT 1</property>
        <property name="checkoutTimeout">2000</property>
        <property name="idleConnectionTestPeriod">30</property>
        <property name="initialPoolSize">5</property>
        <property name="maxIdleTime">18000</property>
        <property name="maxPoolSize">500</property>
        <property name="minPoolSize">5</property>
        <property name="maxStatements">20</property>
        <property name="testConnectionOnCheckin">true</property>
        <property name="unreturnedConnectionTimeout">60</property>
        <property name="debugUnreturnedConnectionStackTraces">true</property>

Screenshot of my current connection pool situation is below:

You can see in Image only 27 connections are currently present in connection pool, while my maxPoolSize is 500, still I am unable to make more connections.

Can someone figure it out while I am getting this exception?

来源：https://stackoverflow.com/questions/38994849/unable-to-get-jdbc-connection-but-only-10-of-available-connections-are-being-us