設置log_format，添加request_time，$upstream_response_time，位置隨意
og_format main '"$request_time" "$upstream_response_time" $remote_addr - $remote_user [$time_local] "$request" '
'$status $body_bytes_sent "$http_referer" '
'"$http_user_agent" "$http_x_forwarded_for"';
日志輸出效果：
"0.015" "0.015" 10.1.2.3 - - [20/Mar/2017:04:05:49 +0800] "GET /myApp/servlet/TestServlet HTTP/1.1" 200 52 "-" "Mozilla/4.0 (compatible; MSIE 4.0; Windows NT)" "-"
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筆者在根據nginx的accesslog中$request_time進行程序優化時，發現有個接口，直接返回數據，平均的$request_time也比較大。原來$request_time包含了用戶數據接收時間，而真正程序的響應時間應該用$upstream_response_time。
下面介紹下2者的差別：
1、request_time
官網描述：request processing time in seconds with a milliseconds resolution; time elapsed between the first bytes were read from the client and the log write after the last bytes were sent to the client 。
指的就是從接受用戶請求的第一個字節到發送完響應數據的時間，即包括接收請求數據時間、程序響應時間、輸出
響應數據時間。
2、upstream_response_time
官網描述：keeps times of responses obtained from upstream servers; times are kept in seconds with a milliseconds resolution. Several response times are separated by commas and colons like addresses in the $upstream_addr variable
是指從Nginx向后端建立連接開始到接受完數據然后關閉連接為止的時間。
從上面的描述可以看出，$request_time肯定比$upstream_response_time值大，特別是使用POST方式傳遞參數時，因為Nginx會把request body緩存住，接受完畢后才會把數據一起發給后端。所以如果用戶網絡較差，或者傳遞數據較大時，$request_time會比$upstream_response_time大很多。
所以如果使用nginx的accesslog查看php程序中哪些接口比較慢的話，記得在log_format中加入$upstream_response_time。