I saw a post recently from Hugo Shebbeare that reminded me of something that I’ve seen asked often on the forums. One thing that I preach to people is that they should use their blog to show what they know, and in this case I want to do that. Also, I remind people to give credit to the inspiration, as I’ve done with the link to Hugo above.

Database mirroring has automatic failover if you have newer SQL Server clients. Those of you with Vista or Windows 7 should be fine, though XP might need an update. SQL Server 2005 started distributing a client that would handle automatic failover, and it does this through the connection string. Here’s a typical one:

Server=DBServer01;Database=Sales;Connection Timeout=30;Integrated Security=SSPI;Failover Partner=DBServer02

In this string we have our main database instance (DBServer01) and the database (Sales). Our mirror server is called DBServer02, and the database name on this server would be the same. Note that you can use IP or named instances as in DBServer01\Sales as well for the connection strings.

If the client has issues connecting to the primary, when the Connection Timeout passes, it will try to connect to the mirror server and start working there. Note that if you had a transaction in progress when the failure occurred, your application has to reconnect to the other server and resubmit the batch.