nginx : Its Multithreaded but uses multiple processes?

I'm trying to understand what makes Nginx so fast, and I have a few questions.

As I understand it, Apache either spawns a new process to serve each request OR spawns a new thread to serve each request. Since each new thread shares virtual address space the memory usage keeps climbs if there are a number of concurrent requests coming in.

Nginx solves this by having just one listening process(Master), with a single execution thread AND 2 or 3(number is configurable) worker processes. This Master process/thread is running an event loop. Effectively waiting for any incoming request. When a request comes in it gives that request to one of the worker processes.

Please correct me if my above understanding is not correct

If the above is correct, then I have a few questions:

1.) Isn't the worker process going to spawn multiple threads and going to run into the same problem as apache ?

2.) Or is nginx fast because its event based architecture uses nonblocking-IO underneath it all. Maybe the worker process spawns threads which do only non-blocking-IO, is that it ?

3.) What "exactly" is "event based architecture", can someone really simplify it, for soemone like me to understand. Does it just pertain to non-blocking-io or something else as well ?

I got a reference of c10k, I am trying to go through it, but I don't think its about event based arch. it seems more for nonblocking IO.

How to enable gzip?

I have found a couple of tutorials on how to enable gzip, btu nothing seems to be working for me, so my question is how do i enable gzip. I am on a shared Dreamhost server, It is running PHP version 5.2, and Apache, from the php info i have found this line, maybe this could help?

zlib

ZLib Support    enabled
Stream Wrapper support  compress.zlib://
Stream Filter support   zlib.inflate, zlib.deflate
Compiled Version    1.2.3.3
Linked Version  1.2.3.3

Directive   Local Value Master Value
zlib.output_compression Off Off
zlib.output_compression_level   -1  -1
zlib.output_handler no value    no value

I have also found this line

_SERVER["HTTP_ACCEPT_ENCODING"] gzip, deflate

I don't know if that has anything to do with it. But that is my first question, secondly, i have dropbox, hosting a javscript file, and I am wondering is it possible to have that file gzipped, It is not being transfered compressed, so is ther any way to do so?

Dynamically update Apache config "allow from IP" without a restart/reload?

My goal is to allow access to an Apache 2.2 forwarding proxy to the IPs of logged-in users only, while denying all other IPs.

In the proxy virtual host, I've successfully included an "allow from" file that gets dynamically rewritten every time a user logs in or out of the site (adding the IP of logged-in users while deleting the IP of logged-out users). However, this requires a graceful restart/reload of Apache to take effect, and I'm looking to improve the performance if I can... because as the user logs in and is transported to the main page, occasionally Apache is right in the middle of the restart and issues a "busy" warning.

I suppose that I could delay the graceful restart of Apache by a second or two to ease the stress on the initial log-in, but if there is a way to avoid the restart altogether, I'd really appreciate knowing about it. Thanks!

node.js running alongside Apache PHP?

I am trying to get my head round node.js...

I am very happy with my LAMP set up as it currently fulfils my requirements. Although I want to add some real-time features into my PHP app. Such as showing all users currently logged into my site and possible chat features.

I don't want to replace my PHP backend, but I do want scalable real-time solutions.

1. Can I throw node.js into the mix to serve my needs without rebuilding the whole application server-side script?

2. How best could node.js serve my 'chat' and 'currently logged in' features?

Great to hear your views!

W.