request_time exstreamly larger than upstream_response_time for some queries when using fastcgi

[Tian Chao]

Hi，
I run python in backend, and use nginx to proxy queries to python by using 
fastcgi. I found some strange things in my nginx log those days. Some queries' 
$request_time are up to 40 seconds which their $upstream_response_time are less 
than 1 second.

Here is my fastcgi related conf.
fastcgi_max_temp_file_size 0;
fastcgi_param PATH_INFO $fastcgi_script_name;
fastcgi_param SCRIPT_NAME "";
fastcgi_pass python_backend;
fastcgi_buffers 1024 8K;

Do you guys know what's the problem?

Chao
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