Major Description
We've spotted exactly the same problem as described in POOL-303 for a pool using mariadb-connector-j-2.1.2 with a pool configured to a size, which exactly reflects the normal quantity of used DB connections.
After weeks of monitoring the situation, we were able to see the same problem as described in POOL-303. After some more drilldown efforts we concluded, that the problem is triggered, because mariadb-connector-j throws instances of Throwables derived from java.lang.Error, which are not instances of java.lang.Execption.
This leads to a leak of makeCount in GenericObjectPool.create(), because makeCount is only decremented, when an instance of java.lang.Exception is thrown and not when an instance of java.langError is thrown.