max_clients and keep alive

[Maxim Dounin]

Hello!

On Mon, May 18, 2009 at 09:54:34AM +1000, Tristan Griffiths wrote:

> Hello,
> 
> Trying to better understand the worker_processes and worker_connections
> settings.
> 
> We have always run Nginx with worker_processes 4 and worker_connections
> 1024 on a dual Xeon 2.4GHz with Hyper Threading. In the documentation,
> it suggests it is better to run worker_processes 2 and
> worker_cpu_affinity 0101 1010 for a dual HTT machine but according to
> the formula (max_clients = worker_processes * worker_connections) that
> would effectively halve the connections we can support to clients and
> backend servers.
> 
> We regularly see more than 2000 keep alive connections at any point in
> time, so do keep alive connections count towards the maximum client
> connections?

Yes.

Feel free to increase worker_connections.  Note also that worker 
connections are cheap - they consume only about 200 bytes of 
memory per connection, so setting something like 16384 isn't a 
big deal.

The only thing to keep in mind is that your OS settings should be 
tuned as well or this may lead to bad results.  E.g. make sure 
that worker_connections are less than available to nginx process 
number of file descriptors (kern.maxfilesperproc under FreeBSD).

Maxim Dounin