客户端不需要使用数据库镜像的证人......

SQL Server 2005引入了已等待已等待的数据库镜像功能。好的，所以我们不得不等待SP1进行官方支持，并为SQL Server 2008进行一些增强功能，如更好的性能和自动修复。如果您需要在没有群集费用的情况下需要数据库的故障转移，则仍然是一个很棒的功能。数据库镜像的一个令人惊讶的方面是客户将透明地重定向自己，无论我们使用什么模式。数据库镜像的默认模式是高可用性。这需要三个SQL Server实例来播放主体，镜像和证人的角色。主体托管可更新的主体数据库，镜像将同步镜像数据库主持，并且证人确定需要自动故障转移。校长和镜子需要是标准版或以上。证人可以是任何版本，包括快递版。校长上的更新与镜像同步到镜像在故障转移期间，没有丢失数据 - 保证。 If you do not require automatic failover, you can dispense with the Witness role and use High Protection mode. Manual failover is still available and again there is no loss of data during failover because of synchronous updates between principal and mirror. If the synchronous updates are causing performance issues you can use High Performance mode which allows asynchronous updates between principal and mirror databases. This means that a commit on the principal does not have to wait for the two-phase commit from the mirror. The principal can continue undeterred while the mirror catches up; however in this mode there is no guarantee that some last minute transactions may not be lost during a failover. Because there is no Witness option in this mode, only manual failover is available. But what about the client connections? They will actually redirect themselves using a process called Transparent Client Redirection assuming you are using the SQL Native Client or ADO.Net 2.0 or above. This is because the connection string now has two slots, one for the default Server Name and one for the “Failover Partner”. If one doesn’t work then it will try the second. This works independently of the Witness so is available for all three modes of Database Mirroring. To me, this was a surprising bonus to the Database Mirroring feature. It just goes to show that if you don’t have a witness, you can simply look in the mirror. Cheers Brian