Apache 访问日志中的 %D 字段 - 第一个字节还是最后一个字节？
Apache Httpd 手册中有一个关于自定义访问日志格式的部分。这些选项之一是 %D 字段，其记录为
处理请求所花费的时间（以微秒为单位）。
谁能告诉我这到底是在测量什么？例如，它是第一个字节的时间，还是最后一个字节的时间，或者比这更复杂的东西？
我需要这是证明符合性能要求，并且我想确切地知道这里测量的是什么。
The Apache Httpd manual has a section on custom access log formats. One of these options is the %D field, which is documented as
The time taken to serve the request, in microseconds.
Can anyone tell me what exactly this is measuring? Is it time-to-first-byte, or time-to-last-byte, for example, or something more complex than that?
I need this is demonstrate compliance to performance requirements, and I want to know exactly what's being measured here.
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它是最后一个字节，或者更确切地说，是在记录阶段计算出的
apr_time_now() - request_rec->request_time。该阶段发生在处理周期的最后，即发送响应之后。It's the last byte or rather,
apr_time_now() - request_rec->request_timewhich is worked out during the logging phase. That phase happens last in the processing cycle, after the response has been sent.http://code.google.com/p/mod-log-firstbyte/ 似乎暗示 %D 测量到最后一个字节的时间，而 mod-log-firstbyte 测量到第一个字节的时间。
http://code.google.com/p/mod-log-firstbyte/ seems to imply that %D measures the time to last byte, whereas mod-log-firstbyte measures the time to first byte.
了解这两个值对于性能调试都很有用。
到第一个字节的时间是连接的等待时间或延迟，而 %D 还包括传输时间。
总时间是您用于总体性能和容量规划的时间，而等待时间是您尝试尽量减少的时间。
Both values are useful to know for performance debugging.
Time to first byte is the wait time or latency of the connection, while %D also includes the transfer time.
The total time is what you use for overall performance and capacity planning, while the wait is what you try to minimize.