max pool size with 12.1.0.2 version

Hi,

On linux x84-64 RH 6.4 

We use a Tomcat application with DB oracle version 11.2.0.4. The pool value was set to 20 in the database.yml uses to establish the connection to the DB instance. everything run fine .

As we changed to oracle DB 12.1.0.2 version (without change nothing in Tomcat application), we had to increase the "pool" parameter value into the database.yml file. (tomapp/webapps/app/WEB-INF/config)

again an error ActiveRecord::ConnectionTimeoutError (could not obtain a database connection within 5 seconds (waited 5.001 seconds). The max pool size is currently 20; consider increasing it.):

Question:

could you explain that please ? is a know problem with DB 12.1.02  ? we would like to understand the reason of that.