I have a question about database connection in Magento I would like to use a primary database to read and write data and if this database will have a problem and goes offline, I would like to use another database to read and write data. Is possibile to configure two database in local.xml?
It is not possible to configure Magento to check a second server when the first server fails. The only configuration that is possible thru the local.xml configuration is specifying a read/write (master) and read-only (slave) connection.
To have Magento write to a backup database you will need to configure a database cluster with multiple masters and assign a floating IP or load-balancing solution that uses a single IP address. The load-balancer then directs the requests to one of the MySQL servers, in case a server fails the load-balancer disables this server and only directs traffic to the other available servers.
See http://severalnines.com/mysql-load-balancing-haproxy-tutorial for details on how to configure HA-Proxy as a load-balancer for MySQL.