Does Nginx have separate queuing mechanism for requests?

Question

Consider the following situation: you are deploying application that can serve 1 req./sec. What would happen if I send 10 request in 1 second? I wrote simple app to test that: https://github.com/amezhenin/nginx_slow_upstream . This test shows that your requests will be served _in_exact_same_order_ they were sent.

For now, this looks like Nginx have some kind of queue for requests, but my colleague(administrator) sayd that there is no any queues in Nginx. So I wrote another question about epoll here: Does epoll preserve the order in which fd's was registered? . From that discussion I figured that epoll does preserves the order of requests.

I have two questions:

1) Is there any mistakes in reasoning/code above?

2) Does Nginx have some sort of queue for requests on top of epoll? Or Nginx uses pure epoll functionality?

Thank you, and sorry for my English :)

Alicaalicante

Answer 1

Nginx doesn't have it own queue, instead it pushes all requests to the application server, which have a listen socket:

#include <sys/types.h>
#include <sys/socket.h>

int listen(int sockfd, int backlog);

(http://linux.die.net/man/2/listen)

backlog defines the length of this queue. You can read the full conversation here.

Alicaalicante

Perhaps I'm not following you properly, but it sounds to me based on this page that NGINX has its own queue: nginx.com/blog/rate-limiting-nginx Can you explain if I'm missing something? – Tamer