In traditional Web application development, server response time is the primary focus for performance analysis.
在传统的Web应用程序开发中，服务器响应时间是性能分析的主要重点。
Lag time: the time the secondary server requires to confirm communication from the primary server.
Lag time：备份服务器确认来自主服务器的通信所需的时间。
If the primary server is unavailable, but the client still has network connectivity, you want to fail over to a secondary server as opposed to using system time.
如果主服务器不可用，但客户机尚具有网络连接，就需要故障转换到备用服务器，而不是使用系统时间。
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