[syslog-ng] Architecture redundancy

Hi, I would like to setup two syslog server so that I don't need to have outage if I need to do some update/upgrade on the system, my questions is how should I set it up? I can send all the traffic to both servers, but I can only load the data to a database on one system at a time. If I need to down the primary system, that mean I need to switch to the secondary to load the data and switch it back when primary is up again. How I can make sure I get all the data load on the database and make sure the syslog data on both servers are the same? Thanks. Hermann