title: How to allow Tomcat to connect to more than one Databases?
body: <p>We have two production databases that have the same data, and a tomcat server currently will connect to one of them to serve a webservice.</p>
  
  <p>The production databases will be updated on at a time (taking quite some time to do so). So to minimise the downtime we will have to manually switch to the other database when running the updating. It is quite cumbersome process. </p>
  
  <p>So the question is is there any load balance/fault tolerance in the DataSource layer to allow this happen automatically? i.e., When one database is down, the other one is used automatically.</p>
  
  <p>We are using Oracle database, also wonder if it is something can be done in the database connection layer.</p>
  
  <p>To clarify, we only need read access to the database, so no transaction is involved.</p>