First let me clear that I am talking about PHP running as FastCGI or using PHP-FPM i.e. webserver and php-interpreter are differently loaded in memory and static files can be served without any putting any load on php-interpreter.
Also nginx is my webserver whose memory footprint is 10-20 times smaller than php-interpreter.
For page-caching module, we have been given so many options to choose from.
I am bit concerned about which one is better - APC or Disk-based?
APC stores cached content in RAM and RAM is faster than hard-disk.
But if we take close look, in APC mode, page requests reaches php-interpreter whereas hard-disk based requests are served alone by web-server reducing load on php-interpreter completely.
Another thing to notice is that as APC is enabled, with page-cache, opcode cache is also there, which mean CPU is less loaded in serving requests to php-interpreter.
Now, I am confused as which will be more scalable (in terms of Digg-like traffic spike)
+1 Cached pages are stored in RAM
-1 php-interpreter is involved in serving requests
+1 Zero load on php-interpreter if page is already cached
-1 Disk is slower than RAM
I hope I am able to convey my question in detail.
If anyone needs more details, please ask. I really want to dig deeper into this topic.