apache 启用apache响应时间日志指令的性能影响
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Performance effect of enabling apache response time log directive
提问by makeyourownmaker
What affect will enabling the response time (%D) LogFormat directive have on apache performance?
启用响应时间 (%D) LogFormat 指令对 apache 性能有什么影响？
The response time is the time taken to serve a request in microseconds.
响应时间是为请求提供服务所花费的时间（以微秒为单位）。
Response time can be enabled like so:
可以像这样启用响应时间：
#LogFormat "%h %l %u %t \"%r\" %>s %b" # Default LogFormat
LogFormat "%h %l %u %t \"%r\" %>s %b %D" # LogFormat including response time
I have written a tool for monitoring and analysing backend script performance, apache-response-time, which requires response time data. I would like to warn potential users how enabling this directive will affect apache server performance.
我编写了一个用于监控和分析后端脚本性能的工具 apache-response-time，它需要响应时间数据。我想警告潜在用户启用此指令将如何影响 apache 服务器性能。
回答by covener
Probably not worth considering in terms of HTTP responses -- only the overhead of 1 addl gettimeofday() call (and a few function calls) so something on the order of a few microseconds. Apache already notes the same thing when the request arrives.
在 HTTP 响应方面可能不值得考虑——只有 1 addl gettimeofday() 调用（和一些函数调用）的开销，所以大约几微秒。当请求到达时，Apache 已经注意到了同样的事情。
http://www.atl.lmco.com/projects/QoS/POSIX_html/index.htmllists some old microbenchmarks of gettimeofday() itself.
http://www.atl.lmco.com/projects/QoS/POSIX_html/index.html列出了 gettimeofday() 本身的一些旧微基准测试。
