keepalive and workers

[Mansoor Peerbhoy]

Hi Mike,
I didn't completely understand your setup, but answers to some of your questions:

- If a connection is kept alive, is it handled by the same Nginx
worker when new requests come in?

Yes, the worker process that is elected to serve a keep-alive HTTP connection will continue to serve all subsequent HTTP requests over that same connection

- Will I have any performance gain if I keep connections from app
server to other servers instead of opening/closing them with every
request from a user?

As Regards "App server to any other server" is concerned, in general, when you are using keep-alive, you should consider how the web server handles keep-alive connections. Some server models would tie down a worker process or thread to a particular connection, and as long as that connection is active (the connection in your case being keep-alive), then that will tie down the server thread, so keep-alive works best if there is a steady stream of web-traffic. If the traffic is sporadic (or in bursts), you may want to consider using Connection:close

Regarding NGINX, if NGINX is at the server end, keep-alive or no keep-alive will not make much performance difference to NGINX, because NGINX worker processes handle requests "on-demand", i.e. in an asynchronous manner. 

NGINX workers do not fork or create new threads upon receipt of a new connection, they simply add the new connection (along with the requisite timeout) to their connection set, and go back to their main select/poll loop.

When interesting events happen on the connection (such as HTTP request received, or POP/IMAP connection received), then NGINX workers process the necessary work required for that connection, and go back to their select() loops. So NGINX will not be affected very much by keep-alives versus non-keepalives. 

Your network, however is a separate issue. non-keepalive (default for HTTP/1.0) implies that the TCP handshake be completed for each HTTP request.


HTH
Mansoor




----- Original Message -----
From: "Michał Jaszczyk" <jasiu85 at gmail.com>
To: nginx at sysoev.ru
Sent: Monday, July 7, 2008 4:00:05 PM GMT +05:30 Chennai, Kolkata, Mumbai, New Delhi
Subject: keepalive and workers

Hi,

I'm creating a website with Nginx and have some questions. When a user
comes with a request, my application server has to connect to many
other servers in order to create the response. Due to separation of
concerns pattern, application server and all other servers are
separate HTTP servers, each built with Nginx. Okay, so this is the
situation I'm in (hopefully my description was clear :) ), and now
come the questions:

- Will I have any performance gain if I keep connections from app
server to other servers instead of opening/closing them with every
request from a user?

- Can I set keepalive in Nginx to last forever?

- If a connection is kept alive, is it handled by the same Nginx
worker when new requests come in?

Regards,

Mike