Hi,

I'm running a simple nginx->memcache->backend architecture, and I'm currently facing some backend problems.

While debugging the situation I've run on some strange log entries which look like nginx was incorrectly giving the summary request_time value :

91.180.100.2 www.mydomain.com "23/Oct/2011:22:30:05 +0200" "10.1.0.41:11211 : 10.1.0.48:90" "GET /images/footer-simple.gif HTTP/1.1" 200 (404 : 200) UP_RESPONSE 0.001 : 60.001 request_time 120.004

So, nginx check's for content in memcache, memcache (10.1.0.41) gives 404 in less than 1ms, then nginx goes to the overloaded apache backend, which gives 200 status content in 60 seconds. What bothers me is the $request_time value, which shows that it took's 120second for nginx to handle the request, and it's not the sum of memcache and backend request_time.

For example I'm giving you another log entry where nginx evaluates the value correctly:

91.180.100.1 www.mydomain.com "23/Oct/2011:21:11:03 +0200" "10.1.0.41:11211 : 10.1.0.48:82, 10.1.0.46:82" "GET /?zanpid=1563268107744039936 HTTP/1.1" 301 (404 : 502, 301) UP_RESPONSE 0.001 : 67.387, 35.46
6 request_time 102.854

Here you see that memcache + backends reponse values are equal to the $request_time value, and this is what I see in my logs by default, the problematic situation occurs very rarely.

Here is my logformat:
log_format upstream '$remote_addr $host "$time_local" "$upstream_addr" "$request" $status ($upstream_status) UP_RESPONSE $upstream_response_time request_time $request_time';

Anybody can explain that behaviour?


Greetz,
Rafal Sawer