Hi Santhosh,
I don' t think the db.connectionPool.maxSize is related to this issue. I won't go into detail here...but the DB_TRIG is not creating a persistent connection. To verify this you could always try setting it to 20. I would set this back to the default.
I think it may be best to open a case. Someone will probably need to look at the agent logs.
Did someone look at Oracle database and see what triggers are getting set?
If you would like you can give me a call.
214-473-1191