In isConnected method in class JDBCContentStore and JDBCDescriptorsStore there 
is added BIG performance overhead on checking if connection is valid. It is 
checked not only if connection is present but also by doing several unnecessary 
calls:

 public boolean isConnected()
         throws ServiceAccessException {
         try {
             if ((connection == null) || 
             (connection.isClosed())) //NOT NEEDED{
                 return false;
             }
             
             PreparedStatement statement = 
                 connection.
prepareStatement(getDatabaseConnectionTestStatement());//NOT NEEDED
             statement.executeQuery();//NOT NEEDED
             statement.close();//NOT NEEDED
             
             // testStatement executed without throwing an exception
             return true;
             
         } catch (SQLException e) {
             throw new ServiceAccessException(this, e);
         }
     }

Normal DB software does not check validity of connection. Slide running on DB 
spends on this most of its time.